Statistical Evaluation of Female Fertility

Statistical Evaluation of Female Fertility M. James Whitelaw, M.D.

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only within recent years that a few demographers,1-3 followed by several clinicians,4-7 have investigated some phases of the statistical aspects of human fertility. One of the latter reports 6 has been criticized on the grounds that the series was too small, as well as not representative. It was also felt that the information obtained in the early puerperium was perhaps not as reliable as that secured in early pregnancy. In order to correct the first objection, I have extended the series to 850 postpartum white patients. The study has been made more representative of the white population of the United States as a whole by including, besides the urban university series, a larger suburban group living in an agricultural-manufacturing county which has witnessed an influx of 1200 new families from the East each month over the past year. As will be shown subsequently, the racialreligious distribution also is fairly representative of the country. The patients were composed of two groups, the first consisting of 250 white, consecutively-interviewed, postpartum, clinic and private patients at the University of California Hospital, San Francisco, between the ages of 20 and 34, and married a minimum of 24 months. They were seen on days 1-4 post partum. The second series, completely and consecutively interviewed by the author, consisted of 600 white private patients of 90 practicing physicians in Santa Clara County, Calif. This group covered the same age T HAS BEEN

From the Department of Obstetrics and Gynecology, University of California School of Medicine, San Francisco, Calif., and San Jose Hospital, San Jose, Calif. This paper was presented at the Thirteenth Annual Meeting of the American Society for the Study of Sterility, New York, May 31-June 2, 1957. The study was made possible by a grant from Smith, Kline & French Research Foundation. The author wishes to express his deepest appreciation for the cooperation of the Obstetrical Staff of the University of California Hospital and for the 90 private physicians of San Jose, without whose aid this study never could have been consummated. 428

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range as that at the University of California and were interviewed in their rooms on the obstetrical floor of the San Jose Hospital, San Jose, Calif. Only 2 patients of the series of 850 were previous patients of the author; none was delivered by him. These 2 infertility patients and 3 others, or 5 in all, were the only ones of the 850 who had had an infertility check. It took 9 months to obtain the 250 cases at the University of California Hospital, but only 5 months for the San Jose group. Every attempt was made to interview patients on day 1 or 2 post partum, for reasons which will be discussed later. The interview was done at the bedside as it was found impractical to take patients from their wards or semiprivate rooms to an isolated cubicle. Before beginning the interrogations, the 850 patients were given a written statement explaining the reason for the survey, and informing them of the permission of their doctor for the interview and their right to refuse to answer at any time during the interrogation. Forty-six of the 646 patients of the San Jose group, either before or during the questioning, took advantage of this clause, while 8 of the 258 at the University of California abstained. The interviews lasted about 30 minutes; all data were recorded during this time on a card devised by the Cancer Research Division of the Universityof California Hospital. Refusal to be interviewed was caused mainly either by the husband being present at the time and adviSing his wife to abstain (after reading the form) or by a semi-private or ward post partum patient who, having been interviewed the previous day, and finding the question objectionable, influenced the others in the room to abstain. In one instance one patient influenced 3 to abstain. The exact method used in this study has been previously described, as well as the type of information that was obtained, and the card system used. 6 There is ample evidence, as will be shown later, that this study gave accurate information of fertility in these two groups, such that the author believes that data obtained under different circumstances might well be misleading and inaccurate. Of 850 in the series, there were 31 multipara patients who admitted to having their first child out of wedlock. There was no more difficulty in obtaining the frequency of coitus and length of time necessary for conception to occur previous to marriage in these than there was in the other 819 women so it was felt that they should not be excluded, as was suggested by Tietze. The ability of the questioner to obtain such information from a patient he has never seen can be considered a reflection of the accuracy of the data

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obtained. This can be reinforced by the fact, as noted above, that refusals were most common where patients had been subjected to the outside advice of their husbands or others, and who had had time to reHect on what they had said. That amnesia may persist through the first day post partum in a large percentage is well known. This was borne out by the few patients whom the author had the opportunity of talking to several mOl'ths after the original interview. They all had little idea of the type of question originally asked. Largely because of the natural tendency of most mothers to avoid telling the physician that pregnancy was due to a miscalculation or failure in a method of contraception, statistical data obtained (except under the unusual circumstances such as exist post partum) are probably not too accurate. It was also noted that unless specifically asked, patients seldom voluntarily gave coitus interruptus as a method of birth control. The various other factors such as illness of either partner, operations, etc., were also voluntarily given only under direct questioning. NO. OF CASES

"5 :

1

.....

2 3

4

4 5

• 7

8 9

~ to;:

10

~

11

~

12

miilll HIGH PRIMARY FERTIliTY. .... . 487

mrrn _ APPROX.

" I 11.1 Z4

HIPIfIH PRIHARY FERTILITY... 7.7 LOW PRIMARY FERTILITY. . . . . 178

EA~H

DAY

Fig. 1.

Distr:bution of pregnancies.

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RESULTS Aspects such as the husband's occupation, surgery, family history, diabetes, birth weight, abortions, etc., which were obtained and tabulated will be the subjects of future articles. Four hundred and eighty-one patients or 56.5 per cent conceived in their first pregnancy in one month or less; 65 conceived in 2 months, 47 in 3 months, 41 in 4 months, 18 in 5 months, and 20 in 6 months, giving 22.4 per cent in from 2 to 6 months. From 7 through 12 months the number of first pregnancies were respectively 13, 10, 13,6, 3, and 19, or 7.6 per cent in from 6 months to a year. The remaining 115 women took over one year to conceive, the longest taking 118 months; these represented 13.5 per cent of the total. As was pointed out in an earlier article, women were classified as being of high primary fertility if their primary pregnancies took place within the first month. If the primary pregnancy ensued after the first month but before the seventh, it was considered medium primary fertility, while all conceptions taking place in over 6 months were tabulated as low primary fertility

E3

HIGH PRIMARY FERTILITY

hiiii~!i~¥"d LOW PRIMARY FERTILlry

430 ? CASES

131 CASES LOW Znd FERTILITY

HIGH 2nd 56 CASES FERTILITY 42.' %

51 CASES

11.8% ' -_ _ _ _ 481 CASES Fig. 2.

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178 CASES

Change in fertility with second pregnancy.

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LOW PRIMARY FERTILITY [J]]] HEDIVM PRIMARY FERTILITY ~n~i{i:ii!iixi

HIGH PRIMARY FERTILITY

186 CASES

184 CASES

111 CASeS

".

20-24

25-29

30-34

AGE Fig. 3.

High primary fertility in relation to age.

(Fig. 1). Of the 481 patients with high primary fertility, 51 were primipara at the time of the interview. The other 430 patients had had one or more pregnancies. In this latter group only 51 required more than 6 months of exposure for any of their following conceptions. In other words, of these 430 women of high primary fertility, 88.2 per cent retained their high fertility throughout their whole childbearing period up to the age of 34. In the 11.8 per cent (51 women) who shifted in their second pregnancy to low secondary fertility, where more than 6 months of exposure was needed for conception, the abortion rate was 530 per cent higher than in the group that stayed in the high and medium brackets (Fig. 2). On separating the high, medium, and low primary fertility patients into

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433

LOW PRIMARY FERTILITY HEPICIM SECONDARY FERTILITY HIGH SECONPARY FERTILITY

44 CASES

73 CASES

20-24

25-29

61 CASES

30-34

AGE Fg. 4.

Low primary fertility in relation to age.

age groups of 5 years each, we noted that the high primary fertility ratio in those 20 to 24 years of age was 77 per cent; in the 25- to 29-year group, 78 per cent; and in the 30- to 34-year-old group, 79 per cent. There seemed to be no essential difference in high primary fertility from ages 20 to 34 (Fig. 3). Paradoxically, the low primary fertility group of 178 cases showed an increase in their fertility with advance in age. On breaking this group down, we noted that a second pregnancy took place in only 131 of the 178 patients, 47 conceiving only once. In other words, in those of low primary fertility, roughly one-third of the second conceptions took place much sooner than had the first. Because of this, in dividing the low primary fertility patients into three age groups (namely, 20 to 24, of which there were 44; 25 to 29, of which there were 73; and 30 to 34, of which there were 61) we note that 68 per cent stayed in the low fertility group in the 20-24 age bracket,

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while in the age group 30 to 34 only 42 per cent remained, due to a shift in status with succeeding pregnancies (Fig. 4). Only one in 9 in the primary high fertility group had only one child in 2 or more years of marriage, while in low primary fertility it was one in 4-half the rate.

DISCUSSION As has been pointed out, the interrelationship of the time required for conception, and such factors as age, duration of marriage, number of children born, etc., has seldom been investigated. We have available only two studies made by other physicians; the findings on fertility in both are somewhat lower than mine. It is felt to be quite valid to point out that neither of these other series can be considered representative, as one was composed entirely of the private practice of one obstetrician and were wives of white collar and professional workers, and business executives, and three out of five were Jewish. Presumably, a number of the factors that would increase the fertility rates of patients, such as less exposure because of occupationsailor, salesman, etc.-as well as time in service, illness, etc., have not been duly taken into account. Of the 850 patients reported here, 250 were representative of a large urban community-San Francisco-and 600 were from San Jose, which represents an excellent cross section of the suburban agriculturalmanufacturing area. The Santa Clara Valley stands among the first 5 counties of the United States in agricultural income. The husbands of the 850 patients represent all walks of life, approximately 15 per cent representing white collar and professional; the rest are laborers either in industry or agriculture. Only 3 per cent were Jewish; 24 per cent were Catholic; 71 per cent were Protestant; and 1 per cent were of other faiths. One per cent gave no religion, which is fairly representative of a cross section of the population of the United States. Studies based on restricted groups such as visit a birth control clinic are not representative of the population of the United States. The 90 physicians whose private patients were studied included every member of the obstetrical department in the San Jose Hospital, as well as nearly every general practictioner whose obstetrical practice was large. This survey tends to support the original one 6 and underlines the fact that with the first pregnancy, conception takes place at an ever-decreasing rate after the first month of exposure. Only 1 in 5 patients interviewed conceived with her nrst child after 6 months. In this low primary fertility group

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56 of the 131, who became pregnant 2 or more times, changed from low primary fertility to high secondary fertility. It may be doubly argued, therefore, that investigation of primary infertility should begin definitely after only 6 months of failure to conceive, while in secondary infertility, probably sooner. It is highly significant that those in the high primary fertility group tend to remain there throughout their total normal childbearing period of life. Only 51, or about 10 per cent, dropped into· the lower group. Analysis of the abortion rate here, showed one 5 times greater than in those that remain in the high fertility section. It may well be that we are dealing here with a primary germ plasm defect. Of the 178 in the low primary fertility group, only 47 had one child, whereas in the high fertility group of 481, 51 had one child. It is clear, of course, that those of low fertility tend to have very few offspring. This is one more reason for starting therapy early-at 6 months in primary infertility. One patient in 3 who is of primary low fertility has an improvement in her fertility status due presumably to the first pregnancy; whereas only 1 in 8 of the high fertility group dropped into the low fertility group with their second pregnancy. There is no evidence in these statistics to indicate that there is appreciable change in the fertility of highly fertile women from the ages of 20 to 34, contrary to McLeod's findings. 9 In obstetrics, and especially in infertility, we are confronted primarily with patients whose chief complaint is primary infertility. The intention of this paper is to give a partial answer as to the chance of such an individual becoming pregnant in a definite length of time, and her chances of having a second child. In cases of secondary infertility where there has been high primary fertility, the same question can be posed, and here again this survey has made some attempt at a solution.

SUMMARY Eight hundred and fifty postpartum white patients between 20 and 34 years of age, married over 24 months, were interviewed by the author on days 1 to 4 post partum. They were seen consecutively and without previous knowledge of the impending interview. Two hundred and fifty were at the University of California Hospital, San Francisco, and 600 at the San Jose Hospital, San Jose. The latter were the private patients of 90 physicians and represent roughly about 50 per cent of all patients delivered in the above category in a population center of 150,000 during a 5-month period. In their

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first pregnancies, 481 patients (56.5 per cent) conceived within 1 month or less, 195 patients (22.4 per cent) conceived in from 2 to 6 months, while 178 patients (21.1 per cent) conceived in from 7 to lI8 months. Only 3 of these latter patients had had operative procedures for their infertility. One hundred and seventy-four had never had a complete infertility investigation. Of those in the primary high fertility group who had had 2 or more pregnancies, 51 out of 430 took more than 6 months to conceive in their second pregnancy. The abortion rate was 5 times as high in the high fertility group that shifted to the low fertility in the second pregnancies, compared to the rest of the high fertility group. In the primary low fertility group, 131 had 2 or more pregnancies; 56 (43 per cent) conceiving in less than 2 months of exposure. In the primary high fertility group there was no falling off of the fertility rate even up to age 34. 2061 Clarmar Way San Jose, California

REFERENCES 1. BEEBE, C. W. Contraception and Fertility in the Southern Appalachians. Baltimore, Maryland, Williams & Wilkins, 1942. 2. HENRY, L. Fecondite des Mariages: Nouvelle Methode de Mesure. Paris Presses, University of France, 1953. 3. HENRY, L. Rev. Inst. Internat. Statist. 21: 135, 1953. 4. TIETZE, C., et al. Fertil. & Steril. 1 :338, 1950. 5. STONE, A., and WARD, M. E. Fertil. & Steril. 7:1-13, 1956. 6. WHITELAW, M. J. Fertil. & SteriZ. 6:103-111, 1955. 7. LLEWELLYN-JONES, D. Brit. M.]. 2: 180-182, 1953. 8. TIETZE, C. Fertil. & SteriZ: 7:88-95, 1956. 9. McLEOD, J., COLD, R. Z., and McLANE, C. M. Fertil. & Steril. 6: 112, 1955.