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Time of ovulation and prolonged pregnancy
Time of ovulation and prolonged pregnancy MOT01
SAITO,
KEIJIRO
YAZAWA,
AKINORI
M.D.
HASHIGUCHI,
TAKAHIRO NOZOMU
M.D.
KUMASAKA, NISHI,
KOHEI Tokyo,
M.D.
KATO,
M.D.
M.D. M.D.
]aQan
In a prospective study of 110 women who were delivered of live infants following the spontaneous onset of labor, the time was calculated between delivery and (1) the first day of the last menstrual period, and (2) the day on which ovulation had probably taken place. The results ef basal body temperature recordings were used to estimate the day of ovulation. Statistical analysis showed that delay of ovulation was the major contributing cause of apparent prolongation of pregnancy over 295 days.
THE INCIDENCE of prolonged pregnancy has been reported by various investigators as ranging from 3.5 to 13.5 per cent.lm3 In general, although there is no unanimity, a pregnancy has been regarded as prolonged when it exceeds the estimated date of confinement by two weeks.3-5The estimated date of confinement, as calculated by Naegele’s rule, is based on the assumption that pregnancy lasts 280 days from the first day of the last menstrual period (LMP) . The true length of gestation is obviously the interval between the time of fertilization of the ovum and the time of delivery of the conceptus. It is evident that studies on gestational length would be more accurate if the timing of ovulation could be assessed with reasonable From the Department of Obstetrics and Gynecology, Tokyo Medical and Dental Uniuersity HosQita$ Yushima, Bunkyo-ku, and Tokyo Sanitarium Hospital. Supported by grants in aid for Developmental Scientific Research from the Education Ministry, No. 570075, and from Morinaga Milk Company. Received
for publication
May
18, 1971.
31
certainty. Likewise, the concept of prolonged pregnancy may be re-evaluated in view of this. There is considerable variation in the interval between the first day of the LMP and the day of ovulation. Delayed ovulation may result in apparent prolongation of pregnancy. The basal body temperature (BBT) has been accepted as an indicator of the approximate time of ovualtionpS8 The onset of pregnancy can be assessedwith reasonable reliability when BBT recordings are made before and after conception. A prospective study was carried out to ascertain gestational length in 129 patients whose day of ovulation was judged by daily recordings of the BBT. Gestational lengths were calculated from both the first day of the last menstrual period and the day of ovulation to the delivery of a live infant following spontaneousonset of labor. These two different gestational lengths were compared to each other with special emphasison a group of patients whose pregnancies were regarded as prolonged.
32
Saito
et al. Am.
Materials
and
methods
Instructions on BBT recordings were given by staff physicians to patients at the Obstetrics and Gynecology Clinics at Tokyo Medical and Dental University Hospital between 1959 and 1969. Approximately one third of the patients were infertile, either primarily or secondarily. In the great majority of patients, the BBT was recorded for a minimum of 3 cycles before conception and throughout the first trimester of pregnancy. Eight patients with toxemia of pregnancy, diabetes mellitus, multiple pregnancy, or pregnancies terminated by induction of labor or cesarean section were excluded. Eleven patients whose pregnancies ended in abortion, ectopic pregnancy, or premature delivery before 36 completed weeks were also excluded. There were no cases of stillbirth. Thus, of 129 patients, 110 were selected for the present study. Ages ranged from 22 to 39 with a mean of 28.9 years. Ninety-three patients were primiparas and 17 were multiparas. These patients represent a middle-class population of the Tokyo Metropolitan Area. The menstrual intervals of the 110 patients were: ( 1) less than 28 days in 44 patients, (2) between 29 and 35 days in 37 patients, and (3) more than 35 days in 17 patients. The menstrual intervals were irregular, varying from 28 to 40 days in 12 patients. Of 110 patients, 32 were infertile for at least two years. Primary infertility was seen in 16 patients and secondary infertility in another 16 patients, The rest of the patients were essentially healthy without major gynecologic disorders. The duration of pregnancy was calculated from the first day of the last menstrual period and from the day of probable ovulation to the delivery of live infants. These are referred to as LMP-delivery and ovulation-delivery intervals, respectively, in this report. The day of ovulation was determined as the last day of a low-temperature phase, which, in the majority of patients, showed a transient but definite fall. Birth weight and heel-to-head length of the newborn infants as well as placental weight were measured. Apgar scores were
Janua,y J. Ohstct.
1, 1W Gynecoi.
evaluated at one and five minutes after birth. Attention was paid to those characteristics which suggest placental insufficiency. These were wrinkled, dry, and cracking skin, lack of vernix caseosa, and staining of amniotic fluid and membranes by meconium. The data were statistically analyzed by the Student’s t test and chi-square test. Results The distribution of LMP-delivery and ovulation-delivery intervals is illustrated in Figs. 1 and 2. The mean ovulation-delivery interval was 264.2 + 9.9 (S.D.) days. Ninetyfive per cent confidence limits of the mean were 262.3 to 266.1 days. In no instance did the ovulation-delivery interval exceed 285 days. Women who ovulated on the same day of the menstrual cycle showed as much as a 38 day difference in the ovulation-delivery interval. The mean LMP-delivery interval was 281.6 + 12.1 (S.D.) days, the maximum being 318 days with 95 per cent confidence limits for the mean of 279.4 to 283.8 days. The relationship between LMP-delivery and ovulation-delivery intervals is illustrated in Fig. 3. A linear relationship was proved to exist between the two figures when LMPdelivery intervals were within the range of 257 to 294 days. The regression line was calculated as Y = 34.1881 + 0.9365X, the correlation coefficient being 0.764 (p < 0.001) . LMP-delivery and ovulation-delivery intervals were plotted on the abscissas against the ordinates of the day of ovulation in Figs. 4 and 5. Statistical analysis failed to prove the correlation between the values given on the abscissa and the ordinate in each figure except that significant correlation did exist when LMP-delivery intervals exceeded 295 days (Y = 285.5156 + 0.6064X, r = 0.834, p < 0.001). Timing of ovulation. Ovulation occurred with the highest frequency between Days 13 and 15 of the menstrual cycle with the peak on Day 13 when it occurred in 17 per cent of the patients. The mean was 18.0 ?. 8.8 (S.D.) days from the first day of LMP. Ovulation occurred before Day 25 in 87 of
Volrme Number
Time of ovulation
112 1
and prolonged
pregnancy
33
NO. OF PATIENTS
20
-
10
xc co . rl
37
v t-
38
39
40
42
41
43
44
45
LMP-DELIVERY INTERVAL IN WEEKS Fig. 1. Distribution of LMP-delivery intervals in 110 women
NO. OF PATIENTS 30
20
10
-
-
35
36
37
OVULATION-DELIVERY Fig. 2. Distribution of ovulation-delivery 110 patients (79.1 per cent). Among 23 patients whose ovulations occurred after Day 25, the menstrual intervals were more than 35 days in 10 patients and were irregular,
38
40
39
INTERVAL intervals
IN
J!l l
d-
41
WEEKS
in 110 women.
ranging from 28 to 40 days, in 5 patients (Table I) _ The average LMP-delivery interval was significantly longer in the group who ovu-
34
Saito et al.
January Am. J. Obstet.
LMP-DELIVERY INTERVAL
310
-
300
-
290
-
280
-
270
-
IN
1, 1972 Gynecol.
DAYS
260 l
l
. . .
t....1.,,.1....l....I....I...~.,,.I....I....I...:I 240
250
260
OVULATION-DELIVERY Fig. 3. Relationship between exists between 257 and 294 Y = 34.1881 + 0.9365X.
270
INTERVAL
LMP-delivery and days in LMP-delivery
IN
ovulation-delivery interval.
280
DAYS
intervals. Linear relationship Regression line was calculated as
Table I. Day of ovulation and menstrual intervals Menstrual
ovulation
No. of patients
9 - 24 25 - 42
87 23
Day of
Totals Numbers
in
110 parentheses
Less than 28 days
( 6) (11)
42
(5)
31
2 (2)
(17)
indicate
Between 29 and 35 days
44 the
number
(7)
of patients
lated on or after Day 25 than in another group whose ovulation occurred before Day 25, the mean being 292.4 + 15.0 (SD.) and 278.8 + 9.5 (S.D.) days, respectively. No difference in ovulation-delivery interval was noted between the former group and the latter, the means being 261.8 and 264.8 days, respectively (p > 0.05). The infants were divided into two groups according to ovulation-delivery interval. Group 1 included 100 infants whose gestations had lasted from 236 to 275 days. Group
(0)
6 (2) 37 with
prolonged
(2)
intervals More than 35 days
Irregular intervals of 28 to 40 days
7 (1) 10 (4)
7 (0) 5 (3)
17
(5)
12 (3)
pregnancy.
2 included 10 infants whose gestations had lasted from 276 to 285 days. The dividing line of 275 days was derived from the sum of the mean and one standard deviation of the gestational length of the entire group of patients. There was no significant difference in birth weight, heel-to-head length, placental weight, placental/fetal weight ratio, and the incidence of low birth weight (less than 2,500 grams) between the two groups (p > 0.05) (Table II). The incidence of low Apgar
Volume Number
112 1
Time
of ovulation
and
prolonged
pregnancy
35
LMP-DELIVERY
t
280
INTERVAL
IN
a
DAYS
l
- t”ol
I-
260
:
a
l ’
DAY Fig. 4. Relationship between LMP-delivery except when LMP-delivery interval exceeds
interval and day 295 days.
OF
OVULATION
of ovulation.
No correlation
exists
Table II. Ovulation-delivery interval and birth weight, body length, placental weight, and placental/fetal weight ratio Ovulation-delivery interval (days) 236-275 276-285 Totals
I
No. of cases
Birth I
weight (Cm.)
Body
length (cm.)
Placental weight (Cm.)
Placental/fetal weight r&o
100 10
3106 3178
51 493.1 2 269.1”
50.2 50.7
2 2.1 c 1.5"
548.0 612.1
k 99.5 2~ 61.9”
0.1769 0.1926
2 0.0234 + 0.0170*
110
3112
+ 476.7
50.3
2 2.0
552.4
+ 98.6
0.1780
+ 0.0233
‘p > 0.05. scores of less than 7 points at 5 min. after birth was proved, by two-by-two factorial analysis, to be significantly higher in Group 2 than in Group 1 (x2 = 9.578). One case of placental insufficiency syndrome was noted in each group. One neonatal death due to hyaline membrane disease occurred in Group 2. Prolonged pregnancy and ovulation-delivery interval. In the present study, pro-
longed pregnancy was defined as pregnancy that continued beyond Day 295 from the first day of LMP. The number of 295 was obtained by the sum of the mean and one standard deviation of the LMP-delivery intervals in the entire series. The incidence of prolonged pregnancy so defined was 15.5 per cent. This high incidence was due in part to a high proportion of patients with delayed ovulation and to the fact that pregnancies
36
Suit0
et al.
OVULATION-DELIVERY INTERVAL
IN
DAYS
l 0
280
l e
l
:
0 0 l
270
-
m
l
l ,
l 0 .
.
‘0’. -
.
.
.
I.1
. .
.
.
g
e..
.
.
.
:’ .
0
0
l
gP(
260
0
0
-0 a.
se.
:
l 0
l
.
.
l
250 :
l t
. . .
.*
240 l
I....l....l....,....I....,....l.. 10
20
30 DAY
Fig. 5. Relationship exists.
between ovulation-delivery
which were terminated before 36 completed weeks were excluded from the study. Increase in ovulation-delivery interval was noted in the prolonged pregnancy group, the mean value of which was 275.6 days in contrast to 262.1 days in the nonprolonged The ovulation-delivery interval of group. more than 275 days was seen in 7 of 17 patients (41.2 per cent) with prolonged pregnancy, while this interval was seen in 3.2 per cent of the patients with nonprolonged pregnancy (Table III). Application of the correlation coefficient test yielded an r2 value of 3.64 per cent for contribution of ovulationdelivery interval to LMP-delivery interval when LMP-delivery interval was more than 294 days. The result implies that an increase in ovulation-delivery interval is not a major factor causing prolongation of pregnancy. The day of ovulation was much delayed in prolonged pregnancy with a mean of 27.8
interval
OF
40
OVULATION
and day of ovulation.
No correlation
+ 10.4 (S.D.) days, while the mean was 16.7 + 6.0 (S.D.) days in the nonprolonged pregnancy group. Ovulation occurring after Day 25 of the menstrual cycle was seen in 64.7 per cent of the patients with prolonged pregnancy, while 47.8 per cent of the patients with ovulation occurring after Day 25 were found to have prolonged pregnancy. The incidence of prolonged pregnancy among those whose ovulations occurred after Day 25 was not significantly different between a group of patients with regular menstrual intervals of less than 35 days and another group whose menstrual intervals were regular and more than 35 days or irregular, ranging from 28 to 40 days. Significant correlation was proved to exist between proIonged pregnancy and the day of ovulation (r = 0.834, p < 0.001). The r2 value was 69.6 per cent for the contribution of the timing of ovulation to the pro-
Volume Number
Time
112
of ovulation
and
prolonged
pregnancy
37
1
Table III.
Day of ovulation,
prolonged
pregnancy,
and menstrual Menstrual
No. of patients with prolonged pregnancy
Day of ovorlation
25 - 42 Totals Numbers
in
17 parentheses
(7)
indicate
29 and
number
35 dayr
5 (4)
0
2
2
(0)
2
(0)
(0)
7 (4) the
- .-.--
interuals IrWgUlM
Between
Less than 28 days
6 (5) 11 (2)
9 - 24
intervals
of patients
longation of pregnancy. Delayed ovulation was indeed the major contributing factor to the prolongation of pregnancy in the cases reported here. Comment Postdatism is an important clinical entity in obstetrics. A compromised fetal environment, or placental dysfunction, and resultant increase in perinatal mortality rate in relation to the postdatism have been discussed by various investigators.5p g-11 Termination of pregnancy, either by amniotomy or cesarean section, has been advocated on the basis of postdatism alone or when it is associated with the presence of meconium in the amniotic fluid or a drop in the maternal urinary excretion of estriol.21 11-14 Whether one favors termination of pregnancy or not, prolonged pregnancy may be viewed differently when it is considered in terms of ovulation-delivery interval, Some cases of prolonged pregnancy may be named pseudopostdatism when ovulation-delivery intervals fall within “normal” limits while LMP-delivery intervals are prolonged. The length of the menstrual cycle depends upon the timing of ovulation. Menstruation usually starts 15 days after ovulation. Employment of an adjusted date of confinement according to the length of the menstrual cycle may be beneficial.
Stewart’j reported that the average duration of pregnancy as calculated from ovula-
REFERENCES
1. Beischer, N. A., Evans, J. H., and Townsend, L.: AM. J. OBSTET. G'INECOL. 103: 476, 1969.
with
ovulation-delivery
More than 35 days
intervals of 28 to 40 days
1 (1) 4 (2)
0 3 (0,
5 (3) intervals
of more
3 (0) -^than
25.5 days.
tion was 266 to 270 days. In 135 women studied by Stewart, no pregnancy exceeded 285 days from the day of ovulation. The mean value of ovulation-delivery interval \vas 267.4 I 7.6 (S.D.) d ays according to Doeringl6 whose report consisted of 277 women and 269 + 7.6 (SD.) days according to Hollenweger-Mayr17 who calculated from isolated coitus in 851 German women. Following the definition of prolonged pregnancy, in which the number 295 was the sum of the mean value plus one standard cleviation, ovulation-delivery interval of more than 275 days may be called “prolonged.” The incidence of “prolonged” ovulation-delivery interval was 9.1 per cent in contrast to 15.5 per cent prolonged pregnancy in LMP-delivery interval. However, no correlation was noted between the two prolonged groups as seen in Fig. 3. The lack of correlation corresponds to insignificant contribution of o~ulation-delivery interval to LMP-delivery interval (3.64 prr cent) in prolonged pregnancy. Variation in the ovulation-delivery interval is approximately of the same magnitude as that of the LMP-delivery interval. The present study proves that the major cause of prolonged pregnancy, in the. materials presented, is delayed ovulation. The authors are indebted to Drs. N. A. Beischer, W. Locke, and J. C. Weed for reviewing the manuscript and Dr. K. Kamiyama for statistical advice.
2. McClure
Browne,
GYNECOL.
85: 573,
3. Bierman,
J. M.:
J. C.: AX. 1963. Siegel,
E..
J. OBSTET.
French,
F.
E.,
38
4. 5.
6. 7. 8. 9. 10.
January
Saito et al.
and Sionian, K.: AM. J. 91: 37, 1965. Evans, T. N., Koeff, S. T., AM. J. OBSTET. GYNECOL. Lucas, W. E., Anctil, A. D. A.: AM. J. OBSTET. 1965. Palmer: Obstet. Gynecol. Stewart, H. L., Jr.: West. 1949. Stewart, H. L., Jr.: A~II. J. 59: 563, 1950. Frampton, J., and Clayton, Gynaecol. Br. Commonw. Zwerdling, M. A.: Pediatrics
ARI. J.
OBSTET.
GYNECOL.
11.
and Morley, G. W.: 85: 701, 1963. O., and Callagan, GYNECOL. 91: 241,
12.
Survey 4: 1, 1949. J. Surg. 57: 192,
14. 15.
OBSTET.
GYNECOL.
16.
S. G.: J. Obstet. 75: 42, 1968. 40: 202, 1967.
17.
13.
Obstet.
1, 1972 Gynecol.
Racker, D., Burgess, G. H., and Manley, G.: Lancet 2: 953, 1953. Be&her, N. A., Brown, J. B., Smith, M. A., and Townsend, L.: AM. J. OBSTET. GYNECOL. 103: 483, 1969. Davis, E. M., and McKeown, M. J.: Obstet. Gvnecol. Survev 22: 559. 1967. Saling, E.: Arch. Dis. Child. 41: 472, 1966. Stewart, H. L., Jr.: .J. A. M. A. 148: 1079. 1952. Doering, G. K.: Geburtshilfe Frauenheilkd. 22: 1191. 1962. Hollenwdger-Mayr, B.: Z. Geburtshilfe Gynaekol. 132: 297, 1950.
SAITO,
KEIJIRO
YAZAWA,
AKINORI
M.D.
HASHIGUCHI,
TAKAHIRO NOZOMU
M.D.
KUMASAKA, NISHI,
KOHEI Tokyo,
M.D.
KATO,
M.D.
M.D. M.D.
]aQan
In a prospective study of 110 women who were delivered of live infants following the spontaneous onset of labor, the time was calculated between delivery and (1) the first day of the last menstrual period, and (2) the day on which ovulation had probably taken place. The results ef basal body temperature recordings were used to estimate the day of ovulation. Statistical analysis showed that delay of ovulation was the major contributing cause of apparent prolongation of pregnancy over 295 days.
THE INCIDENCE of prolonged pregnancy has been reported by various investigators as ranging from 3.5 to 13.5 per cent.lm3 In general, although there is no unanimity, a pregnancy has been regarded as prolonged when it exceeds the estimated date of confinement by two weeks.3-5The estimated date of confinement, as calculated by Naegele’s rule, is based on the assumption that pregnancy lasts 280 days from the first day of the last menstrual period (LMP) . The true length of gestation is obviously the interval between the time of fertilization of the ovum and the time of delivery of the conceptus. It is evident that studies on gestational length would be more accurate if the timing of ovulation could be assessed with reasonable From the Department of Obstetrics and Gynecology, Tokyo Medical and Dental Uniuersity HosQita$ Yushima, Bunkyo-ku, and Tokyo Sanitarium Hospital. Supported by grants in aid for Developmental Scientific Research from the Education Ministry, No. 570075, and from Morinaga Milk Company. Received
for publication
May
18, 1971.
31
certainty. Likewise, the concept of prolonged pregnancy may be re-evaluated in view of this. There is considerable variation in the interval between the first day of the LMP and the day of ovulation. Delayed ovulation may result in apparent prolongation of pregnancy. The basal body temperature (BBT) has been accepted as an indicator of the approximate time of ovualtionpS8 The onset of pregnancy can be assessedwith reasonable reliability when BBT recordings are made before and after conception. A prospective study was carried out to ascertain gestational length in 129 patients whose day of ovulation was judged by daily recordings of the BBT. Gestational lengths were calculated from both the first day of the last menstrual period and the day of ovulation to the delivery of a live infant following spontaneousonset of labor. These two different gestational lengths were compared to each other with special emphasison a group of patients whose pregnancies were regarded as prolonged.
32
Saito
et al. Am.
Materials
and
methods
Instructions on BBT recordings were given by staff physicians to patients at the Obstetrics and Gynecology Clinics at Tokyo Medical and Dental University Hospital between 1959 and 1969. Approximately one third of the patients were infertile, either primarily or secondarily. In the great majority of patients, the BBT was recorded for a minimum of 3 cycles before conception and throughout the first trimester of pregnancy. Eight patients with toxemia of pregnancy, diabetes mellitus, multiple pregnancy, or pregnancies terminated by induction of labor or cesarean section were excluded. Eleven patients whose pregnancies ended in abortion, ectopic pregnancy, or premature delivery before 36 completed weeks were also excluded. There were no cases of stillbirth. Thus, of 129 patients, 110 were selected for the present study. Ages ranged from 22 to 39 with a mean of 28.9 years. Ninety-three patients were primiparas and 17 were multiparas. These patients represent a middle-class population of the Tokyo Metropolitan Area. The menstrual intervals of the 110 patients were: ( 1) less than 28 days in 44 patients, (2) between 29 and 35 days in 37 patients, and (3) more than 35 days in 17 patients. The menstrual intervals were irregular, varying from 28 to 40 days in 12 patients. Of 110 patients, 32 were infertile for at least two years. Primary infertility was seen in 16 patients and secondary infertility in another 16 patients, The rest of the patients were essentially healthy without major gynecologic disorders. The duration of pregnancy was calculated from the first day of the last menstrual period and from the day of probable ovulation to the delivery of live infants. These are referred to as LMP-delivery and ovulation-delivery intervals, respectively, in this report. The day of ovulation was determined as the last day of a low-temperature phase, which, in the majority of patients, showed a transient but definite fall. Birth weight and heel-to-head length of the newborn infants as well as placental weight were measured. Apgar scores were
Janua,y J. Ohstct.
1, 1W Gynecoi.
evaluated at one and five minutes after birth. Attention was paid to those characteristics which suggest placental insufficiency. These were wrinkled, dry, and cracking skin, lack of vernix caseosa, and staining of amniotic fluid and membranes by meconium. The data were statistically analyzed by the Student’s t test and chi-square test. Results The distribution of LMP-delivery and ovulation-delivery intervals is illustrated in Figs. 1 and 2. The mean ovulation-delivery interval was 264.2 + 9.9 (S.D.) days. Ninetyfive per cent confidence limits of the mean were 262.3 to 266.1 days. In no instance did the ovulation-delivery interval exceed 285 days. Women who ovulated on the same day of the menstrual cycle showed as much as a 38 day difference in the ovulation-delivery interval. The mean LMP-delivery interval was 281.6 + 12.1 (S.D.) days, the maximum being 318 days with 95 per cent confidence limits for the mean of 279.4 to 283.8 days. The relationship between LMP-delivery and ovulation-delivery intervals is illustrated in Fig. 3. A linear relationship was proved to exist between the two figures when LMPdelivery intervals were within the range of 257 to 294 days. The regression line was calculated as Y = 34.1881 + 0.9365X, the correlation coefficient being 0.764 (p < 0.001) . LMP-delivery and ovulation-delivery intervals were plotted on the abscissas against the ordinates of the day of ovulation in Figs. 4 and 5. Statistical analysis failed to prove the correlation between the values given on the abscissa and the ordinate in each figure except that significant correlation did exist when LMP-delivery intervals exceeded 295 days (Y = 285.5156 + 0.6064X, r = 0.834, p < 0.001). Timing of ovulation. Ovulation occurred with the highest frequency between Days 13 and 15 of the menstrual cycle with the peak on Day 13 when it occurred in 17 per cent of the patients. The mean was 18.0 ?. 8.8 (S.D.) days from the first day of LMP. Ovulation occurred before Day 25 in 87 of
Volrme Number
Time of ovulation
112 1
and prolonged
pregnancy
33
NO. OF PATIENTS
20
-
10
xc co . rl
37
v t-
38
39
40
42
41
43
44
45
LMP-DELIVERY INTERVAL IN WEEKS Fig. 1. Distribution of LMP-delivery intervals in 110 women
NO. OF PATIENTS 30
20
10
-
-
35
36
37
OVULATION-DELIVERY Fig. 2. Distribution of ovulation-delivery 110 patients (79.1 per cent). Among 23 patients whose ovulations occurred after Day 25, the menstrual intervals were more than 35 days in 10 patients and were irregular,
38
40
39
INTERVAL intervals
IN
J!l l
d-
41
WEEKS
in 110 women.
ranging from 28 to 40 days, in 5 patients (Table I) _ The average LMP-delivery interval was significantly longer in the group who ovu-
34
Saito et al.
January Am. J. Obstet.
LMP-DELIVERY INTERVAL
310
-
300
-
290
-
280
-
270
-
IN
1, 1972 Gynecol.
DAYS
260 l
l
. . .
t....1.,,.1....l....I....I...~.,,.I....I....I...:I 240
250
260
OVULATION-DELIVERY Fig. 3. Relationship between exists between 257 and 294 Y = 34.1881 + 0.9365X.
270
INTERVAL
LMP-delivery and days in LMP-delivery
IN
ovulation-delivery interval.
280
DAYS
intervals. Linear relationship Regression line was calculated as
Table I. Day of ovulation and menstrual intervals Menstrual
ovulation
No. of patients
9 - 24 25 - 42
87 23
Day of
Totals Numbers
in
110 parentheses
Less than 28 days
( 6) (11)
42
(5)
31
2 (2)
(17)
indicate
Between 29 and 35 days
44 the
number
(7)
of patients
lated on or after Day 25 than in another group whose ovulation occurred before Day 25, the mean being 292.4 + 15.0 (SD.) and 278.8 + 9.5 (S.D.) days, respectively. No difference in ovulation-delivery interval was noted between the former group and the latter, the means being 261.8 and 264.8 days, respectively (p > 0.05). The infants were divided into two groups according to ovulation-delivery interval. Group 1 included 100 infants whose gestations had lasted from 236 to 275 days. Group
(0)
6 (2) 37 with
prolonged
(2)
intervals More than 35 days
Irregular intervals of 28 to 40 days
7 (1) 10 (4)
7 (0) 5 (3)
17
(5)
12 (3)
pregnancy.
2 included 10 infants whose gestations had lasted from 276 to 285 days. The dividing line of 275 days was derived from the sum of the mean and one standard deviation of the gestational length of the entire group of patients. There was no significant difference in birth weight, heel-to-head length, placental weight, placental/fetal weight ratio, and the incidence of low birth weight (less than 2,500 grams) between the two groups (p > 0.05) (Table II). The incidence of low Apgar
Volume Number
112 1
Time
of ovulation
and
prolonged
pregnancy
35
LMP-DELIVERY
t
280
INTERVAL
IN
a
DAYS
l
- t”ol
I-
260
:
a
l ’
DAY Fig. 4. Relationship between LMP-delivery except when LMP-delivery interval exceeds
interval and day 295 days.
OF
OVULATION
of ovulation.
No correlation
exists
Table II. Ovulation-delivery interval and birth weight, body length, placental weight, and placental/fetal weight ratio Ovulation-delivery interval (days) 236-275 276-285 Totals
I
No. of cases
Birth I
weight (Cm.)
Body
length (cm.)
Placental weight (Cm.)
Placental/fetal weight r&o
100 10
3106 3178
51 493.1 2 269.1”
50.2 50.7
2 2.1 c 1.5"
548.0 612.1
k 99.5 2~ 61.9”
0.1769 0.1926
2 0.0234 + 0.0170*
110
3112
+ 476.7
50.3
2 2.0
552.4
+ 98.6
0.1780
+ 0.0233
‘p > 0.05. scores of less than 7 points at 5 min. after birth was proved, by two-by-two factorial analysis, to be significantly higher in Group 2 than in Group 1 (x2 = 9.578). One case of placental insufficiency syndrome was noted in each group. One neonatal death due to hyaline membrane disease occurred in Group 2. Prolonged pregnancy and ovulation-delivery interval. In the present study, pro-
longed pregnancy was defined as pregnancy that continued beyond Day 295 from the first day of LMP. The number of 295 was obtained by the sum of the mean and one standard deviation of the LMP-delivery intervals in the entire series. The incidence of prolonged pregnancy so defined was 15.5 per cent. This high incidence was due in part to a high proportion of patients with delayed ovulation and to the fact that pregnancies
36
Suit0
et al.
OVULATION-DELIVERY INTERVAL
IN
DAYS
l 0
280
l e
l
:
0 0 l
270
-
m
l
l ,
l 0 .
.
‘0’. -
.
.
.
I.1
. .
.
.
g
e..
.
.
.
:’ .
0
0
l
gP(
260
0
0
-0 a.
se.
:
l 0
l
.
.
l
250 :
l t
. . .
.*
240 l
I....l....l....,....I....,....l.. 10
20
30 DAY
Fig. 5. Relationship exists.
between ovulation-delivery
which were terminated before 36 completed weeks were excluded from the study. Increase in ovulation-delivery interval was noted in the prolonged pregnancy group, the mean value of which was 275.6 days in contrast to 262.1 days in the nonprolonged The ovulation-delivery interval of group. more than 275 days was seen in 7 of 17 patients (41.2 per cent) with prolonged pregnancy, while this interval was seen in 3.2 per cent of the patients with nonprolonged pregnancy (Table III). Application of the correlation coefficient test yielded an r2 value of 3.64 per cent for contribution of ovulationdelivery interval to LMP-delivery interval when LMP-delivery interval was more than 294 days. The result implies that an increase in ovulation-delivery interval is not a major factor causing prolongation of pregnancy. The day of ovulation was much delayed in prolonged pregnancy with a mean of 27.8
interval
OF
40
OVULATION
and day of ovulation.
No correlation
+ 10.4 (S.D.) days, while the mean was 16.7 + 6.0 (S.D.) days in the nonprolonged pregnancy group. Ovulation occurring after Day 25 of the menstrual cycle was seen in 64.7 per cent of the patients with prolonged pregnancy, while 47.8 per cent of the patients with ovulation occurring after Day 25 were found to have prolonged pregnancy. The incidence of prolonged pregnancy among those whose ovulations occurred after Day 25 was not significantly different between a group of patients with regular menstrual intervals of less than 35 days and another group whose menstrual intervals were regular and more than 35 days or irregular, ranging from 28 to 40 days. Significant correlation was proved to exist between proIonged pregnancy and the day of ovulation (r = 0.834, p < 0.001). The r2 value was 69.6 per cent for the contribution of the timing of ovulation to the pro-
Volume Number
Time
112
of ovulation
and
prolonged
pregnancy
37
1
Table III.
Day of ovulation,
prolonged
pregnancy,
and menstrual Menstrual
No. of patients with prolonged pregnancy
Day of ovorlation
25 - 42 Totals Numbers
in
17 parentheses
(7)
indicate
29 and
number
35 dayr
5 (4)
0
2
2
(0)
2
(0)
(0)
7 (4) the
- .-.--
interuals IrWgUlM
Between
Less than 28 days
6 (5) 11 (2)
9 - 24
intervals
of patients
longation of pregnancy. Delayed ovulation was indeed the major contributing factor to the prolongation of pregnancy in the cases reported here. Comment Postdatism is an important clinical entity in obstetrics. A compromised fetal environment, or placental dysfunction, and resultant increase in perinatal mortality rate in relation to the postdatism have been discussed by various investigators.5p g-11 Termination of pregnancy, either by amniotomy or cesarean section, has been advocated on the basis of postdatism alone or when it is associated with the presence of meconium in the amniotic fluid or a drop in the maternal urinary excretion of estriol.21 11-14 Whether one favors termination of pregnancy or not, prolonged pregnancy may be viewed differently when it is considered in terms of ovulation-delivery interval, Some cases of prolonged pregnancy may be named pseudopostdatism when ovulation-delivery intervals fall within “normal” limits while LMP-delivery intervals are prolonged. The length of the menstrual cycle depends upon the timing of ovulation. Menstruation usually starts 15 days after ovulation. Employment of an adjusted date of confinement according to the length of the menstrual cycle may be beneficial.
Stewart’j reported that the average duration of pregnancy as calculated from ovula-
REFERENCES
1. Beischer, N. A., Evans, J. H., and Townsend, L.: AM. J. OBSTET. G'INECOL. 103: 476, 1969.
with
ovulation-delivery
More than 35 days
intervals of 28 to 40 days
1 (1) 4 (2)
0 3 (0,
5 (3) intervals
of more
3 (0) -^than
25.5 days.
tion was 266 to 270 days. In 135 women studied by Stewart, no pregnancy exceeded 285 days from the day of ovulation. The mean value of ovulation-delivery interval \vas 267.4 I 7.6 (S.D.) d ays according to Doeringl6 whose report consisted of 277 women and 269 + 7.6 (SD.) days according to Hollenweger-Mayr17 who calculated from isolated coitus in 851 German women. Following the definition of prolonged pregnancy, in which the number 295 was the sum of the mean value plus one standard cleviation, ovulation-delivery interval of more than 275 days may be called “prolonged.” The incidence of “prolonged” ovulation-delivery interval was 9.1 per cent in contrast to 15.5 per cent prolonged pregnancy in LMP-delivery interval. However, no correlation was noted between the two prolonged groups as seen in Fig. 3. The lack of correlation corresponds to insignificant contribution of o~ulation-delivery interval to LMP-delivery interval (3.64 prr cent) in prolonged pregnancy. Variation in the ovulation-delivery interval is approximately of the same magnitude as that of the LMP-delivery interval. The present study proves that the major cause of prolonged pregnancy, in the. materials presented, is delayed ovulation. The authors are indebted to Drs. N. A. Beischer, W. Locke, and J. C. Weed for reviewing the manuscript and Dr. K. Kamiyama for statistical advice.
2. McClure
Browne,
GYNECOL.
85: 573,
3. Bierman,
J. M.:
J. C.: AX. 1963. Siegel,
E..
J. OBSTET.
French,
F.
E.,
38
4. 5.
6. 7. 8. 9. 10.
January
Saito et al.
and Sionian, K.: AM. J. 91: 37, 1965. Evans, T. N., Koeff, S. T., AM. J. OBSTET. GYNECOL. Lucas, W. E., Anctil, A. D. A.: AM. J. OBSTET. 1965. Palmer: Obstet. Gynecol. Stewart, H. L., Jr.: West. 1949. Stewart, H. L., Jr.: A~II. J. 59: 563, 1950. Frampton, J., and Clayton, Gynaecol. Br. Commonw. Zwerdling, M. A.: Pediatrics
ARI. J.
OBSTET.
GYNECOL.
11.
and Morley, G. W.: 85: 701, 1963. O., and Callagan, GYNECOL. 91: 241,
12.
Survey 4: 1, 1949. J. Surg. 57: 192,
14. 15.
OBSTET.
GYNECOL.
16.
S. G.: J. Obstet. 75: 42, 1968. 40: 202, 1967.
17.
13.
Obstet.
1, 1972 Gynecol.
Racker, D., Burgess, G. H., and Manley, G.: Lancet 2: 953, 1953. Be&her, N. A., Brown, J. B., Smith, M. A., and Townsend, L.: AM. J. OBSTET. GYNECOL. 103: 483, 1969. Davis, E. M., and McKeown, M. J.: Obstet. Gvnecol. Survev 22: 559. 1967. Saling, E.: Arch. Dis. Child. 41: 472, 1966. Stewart, H. L., Jr.: .J. A. M. A. 148: 1079. 1952. Doering, G. K.: Geburtshilfe Frauenheilkd. 22: 1191. 1962. Hollenwdger-Mayr, B.: Z. Geburtshilfe Gynaekol. 132: 297, 1950.