Eating or drinking during labor: Is it time to change the rules?

Eating or Drinking During Labor: Is It Time to Change the Rules? Geraldine O'Sullivan, Mark Kubli, and Mark Scrutton "OST PRACTICING anesthetists have never . managed or even observed acid pulmonary aspiration (Mendelson's Syndrome) 1 in a parturient. In the most recent Report on the Confidential Enquiries into Maternal Deaths in the United Kingdom (1994-1996), 2 no mother died as a consequence of pulmonary aspiration. In the last four Confidential Enquiries (1985 to 1996), 3 in which 12-year period there were approximately 9 million births, four mothers died from pulmonary aspiration. However, in two of these mothers there were other complicating factors. Three of the mothers had received parenteral opioids during labor; in the fourth case the use of opioids was not recorded. This is in sharp contrast to the very first Confidential Enquiry (1952-1954), 4 which reported 29 maternal deaths from aspiration (Fig 1). This remarkable improvement can in part be attributed to the greater use of regional anaesthesia, the introduction of the H 2 antagonists, the improved training of obstetric anesthetists, and the policy of fasting women during labor. It could therefore be argued that gastric aspiration is no longer an important clinical issue in obstetric anesthesia and that in the very rare event of a mother aspirating, it is likely that treatment in a modern intensive care unit will ensure her complete recovery. It is not surprising then that midwives, obstetricians, and even mothers themselves are demanding that the unpopular policy of starving women during labor be reviewed.

M

GASTRIC PHYSIOLOGY DURING PREGNANCY

Gastroesophageal Reflux Symptoms of gastroesophageal reflux occur in 80% of women at term, and studies using lower esophageal pH monitoring indicated that even those without symptoms will also reflux gastric contents into the esophagus. 5'6 The progressive increase in intragastric pressure seen during pregnancy, as well as the relaxant effect of progesterone on the smooth muscle of the lower esophageal sphincter, are among the factors responsible for this decrease in gastroesophageal sphincter pressure. The relaxant effect of opioids, benzodiaz-

epines, and anesthetic agents on the upper-esophageal sphincter means that regurgitation into the pharynx and subsequent pulmonary aspiration is a particular hazard for those in whom the protection provided by the lower esophageal sphincter is deficient.

Gastric Secretion Studies of gastric physiology during pregnancy have always been limited by ethical considerations and maternal compliance. In the most comprehensive study of gastric secretion during pregnancy, 7 in which basal and histamine-augmented gastric secretions were measured in 10 controls and 30 pregnant women equally distributed throughout the three trimesters of pregnancy, there was no overall significant difference in the basal rate of gastric acid secretion between the pregnant and the nonpregnant women. However, when the different trimesters were evaluated, the mean rate of basal secretion was lower in women in their second trimester. The rate of gastric secretion in response to histamine was decreased in the first and second trimester groups compared with the third trimester and nonpregnant control groups.

Gastric Emptying Techniques used to measure gastric emptying during pregnancy have included roentgenogram, 8'9 dye dilution with nasogastric intubation, 1~ realtime ultrasound, 11 gastric impedance, 12 and indirect methods such as acetaminophen absorbtion. No technique has shown that pregnancy itself causes a delay in the rate of gastric emptying. From the Department of Anaesthesia, St. Thomas' Hospital, London; and the Department of Anaesthesia, St. Michael's Hospital, Bristol, England. The authors of this article were supported by grants from the Obstetric Anaesthetists Association and the Sir Jules Thorn Charitable Trust. Address correspondence and reprint requests to Geraldine O'Sullivan, MD, FRCA, St. Thomas' Hospital, SE1 7EH London, England. Copyright 9 2000 by W.B. Saunders Company 0277-0326/00/1903-0002510.00/0 doi: 10.1053/sa.2000.9042

Seminars in Anesthesia, Perioperative Medicine and Pain, Vol 19, No 3 (September),2000: pp 157-163

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Fig 1. Trends in maternal mortality from anesthesia and pulmonary aspiration: 1952 to 1966. (Reprinted with permission.) 4

Davison, 1~ using a dye-dilution double-sampiing technique, found that gastric emptying was delayed during labor and that the pattern was no longer exponential. Nimmo et a113"14 studied women in early and late labor using the indirect acetaminophen technique; women in early labor exhibited rapid gastric emptying, whereas those nearer to the time of delivery exhibited delayed gastric emptying. Pain has a delaying effect on the rate of gastric emptying, 15 probably because of the stimulation of the sympathetic nervous system, although endogenous opioids (/3-endorphins and enkephalins) may also play a part. Pain is certainly not the sole cause of the delay in gastric emptying in late labor because Nimmo et al13,14 demonstrated a similar delay in late labor in women who had received either epidural local anesthetic alone or no analgesia. Marathon runners exhibit a delay in gastric emptying, a result perhaps of sympathetic stimulation and the acidosis associated with exercising. The acetaminophen technique can only be employed in fasting subjects, hence the ketosis caused by fasting during labor, in addition to the metabolic consequences of labor itself, could have contributed to the observed delay in gastric emptying.

The delay in gastric emptying seen during labor is markedly potentiated by the use of parenteral opioids. This has been confirmed by both roentgenogram 8'9 and acetaminophen absorption studies. 13 Epidural/intrathecal opioids are now used routinely in modern obstetric analgesia practice. Epidural analgesia using local anesthetic alone causes no further delay in gastric emptying during labor. However, a single epidural bolus of fentanyl, given either during labor 16 or after elective caesarean section, 17 causes a significant delay in gastric emptying. Using the acetaminophen absorption technique, Porter et al TM examined the effect of epidural infusions of local anesthetic and opioid on the rate of gastric emptying during labor. The mean maximum concentration of acetaminophen, the time to maximum concentration, and the area under the curve of acetaminophen concentration plotted against time were calculated for mothers given infusions of either plain bupivacaine or bupivacaine and fentanyl. No delay in gastric emptying was found in mothers receiving up to 100 ~g of fentanyl by infusion; however, when doses of fentanyl in excess of 100 p~g were infused, gastric emptying was delayed.

EATING OR DRINKING DURING LABOR Ethical constraints and patient compliance have meant that acetaminophen absorption has become the most commonly employed technique used to measure gastric emptying during pregnancy and labor. Acetaminophen is not absorbed from the stomach but is rapidly absorbed from the upper small intestine, its absorption therefore being directly dependent on the rate of gastric emptying. ~9 The rate of acetaminophen absorption has been shown to reflect the rate of gastric emptying of liquids when compared with scintiscanning studies, but no correlation has been determined between the half-time of emptying of semisolids and the measurements of acetaminophen absorption. However, roentgenogram studies of the emptying of solid food from the stomach, which today would be ethically impossible, confirm that labor will delay the emptying of a barium meal and that this delay is exacerbated by the use of parenteral opioids.9

INTRAVENOUS FLUIDS DURING LABOR Because of the pregnancy-induced increase in total body water, the pregnant woman is well adapted for periods of water deprivation, and indeed her ability to cope with a water load is impaired. The excessive administration of intravenous (IV) dextrose solutions in labor can result in hyponatremia in both mother and baby2~ these effects are exacerbated by the antidiuretic effect of oxytocin, which is used to induce or augment labor. 21 Most obstetric units now allow mothers to consume clear fluids during labor, and IV fluids are rarely used solely for the purpose of providing hydration or calories. In the past, it was accepted by many that ketonuria during labor warranted treatment in the belief that ketonuria, caused by maternal starvation, would impede the progress of labor and potentially harm the fetus. Metzenger et a122 showed that women in their third trimester who are fasted for 12 hours exhibit a state of "accelerated starvation," with rapid increases in plasma f3-hydroxybutyrate as well as acetoacetic acid and the nonesterified fatty acids from which they are derived and a concomitant decrease in plasma glucose. These changes are then compounded by the metabolic demands of labor and delivery. Dumoulin and Foulkes, 23 in a study of 3,511 women, showed that 40% of them exhibited ketonuria in the course of labor. This increased from 10% in those who labored less than 6 hours to

159 66% in women who labored more than 12 hours. However, the level of these ketones has not been shown to bear any relationship to maternal or fetal acid-base balance. 24 In an attempt to reverse the ketosis observed during labor, it was in the past common practice to administer IV dextrose solutions to the mother. This practice was subsequently abandoned because of its detrimental effects, which included fluid overload and lactic acidosis in both the mother and fetus and rebound hypoglycemia and jaundice in the neonate. 2~ It could also be argued that ketonuria is a normal physiological response to labor, the degree of ketonuria being related to both the duration of labor and maternal fasting. In 1983, Lind 26 observed that "the problems of dehydration, hypoglycemia and ketosis have probably been overstated and have prompted a tendency to give laboring women intravenous fluids unnecessarily." Current anesthetic practice permits, even encourages, the use of clear fluids up to two hours preoperatively. It would seem logical, therefore, to allow mothers free access to clear fluid during the course of labor, and this should include the highrisk mother. Few mothers will require emergency surgery under general anesthesia, and there is no evidence to suggest that the ingestion of clear fluids during labor, in quantities that alleviate thirst, will either increase the risk of aspiration or adversely influence outcome should the mother inhale.

THE DEMAND FOR CHANGE In the United Kingdom, the expanding role of the midwife has been a significant phenomenon in the last decade and has received strong political support. A government document, entitled Changing Childbirth27 and published in 1993, outlined the principles of good maternity care: 1. The mother must be the focus of maternity care. She should be able to feel that she is in control of what is happening to her and able to make decisions about her care, based on her needs, having discussed matters fully with the professionals involved. 2. Maternity services must be readily and easily accessible to all. They should be sensitive to the needs of the local popu-

160 lation and based primarily in the community. 3. Women should be involved in the monitoring and planning of maternity services to ensure that they are responsive to the needs of a changing society. 4. Care should be effective, and resources should be used efficiently.

Changing Childbirth defined its own challenge by targeting indicators of success that were to be achieved by 2000. Many of these related to the increasingly important role of midwives in the care of the mother, including: 1. Every mother should know one midwife who ensures continuity of her care, ie, the named midwife. 2. Midwives should have direct access to some beds in all maternity units. ~ 3. At least 30% of women delivered in a maternity unit should be admitted under the management of the midwife. It was anticipated, therefore, that a significant number of mothers would be managed by teams of midwives and would be delivered in low-risk units attached to the local obstetric hospital or at home. Thus, in modern midwifery management in any part of the world, anesthetic dictates--especially those that do not appear evidence based--are unlikely to be considered relevant or necessary. A mother delivered at home will sit down and eat with her midwife, and should she choose to deliver in hospital she would not expect her freedom of choice to be restricted. Mothers with restricted access to oral fluids during labor find the experience "moderately or most stressful. ''2s The widespread use of regional blockade in obstetrics has reduced the need for general anesthesia. Because the evidence supporting the withholding of fluids or food in the prophylaxis against pulmonary aspiration is somewhat tenuous, it is not surprising that anesthetic protocols are being challenged. The onus is therefore on obstetric anesthetists to justify the protocols they impose on their local delivery unit. An abstract presented by Ludka 29 at a midwifery congress in The Hague in 1987 received widespread coverage in the midwifery literature. The abstract concerned the North Central Bronx Hos-

O'SULLIVAN, KUBLI,AND SCRUITON pital, a New York City municipal hospital serving one of the poorest and most disadvantaged populations in the United States. Midwives were the primary providers of prenatal, intrapartum, and postpartum care for all low-risk mothers, whereas the care of high-risk mothers was shared with the attending obstetricians. Laboring women at this hospital were allowed to eat lightly and drink throughout normal labor as desired. This practice was suspended for a 6-month period during which time the following were claimed: 1. The only case of maternal aspiration occurred in a mother who had taken nothing by mouth in the previous 36 hours. 2. The use of chemicals to stimulate labor increased five-fold. 3. Instrumental deliveries increased by 35%, and the cesarean section rate increased by 38%. 4. Vaginal births after a previous cesarean section decreased by 37%. 5. The need for intensive care of the newborn increased by 69%. As a result of this deterioration, mothers were again allowed to consume a light diet during labor, and the fetal and maternal outcomes returned to their previous levels! It is notable that in this abstract the author quotes percentages and does not provide the hospital's hard data, making it impossible to mount a reasoned challenge to the authors' claims. It is also somewhat naive to consider that maternal and fetal outcomes were influenced only by food and drink. A subsequent article by Haire 3~ confirmed that mothers at the North Bronx Hospital who were not expected to have cesarean sections were allowed to eat lightly if hungry and to drink when thirsty. During a 12-year period with 30,000 deliveries, no case of pulmonary aspiration was seen in any mother who was allowed to eat or drink during labor. Therefore, the mothers who were allowed to eat or drink were carefully selected, and many mothers did not eat or drink during labor. This fact was not mentioned in the abstract by Ludka, 29 which precipitated the demand for feeding during labor. Many have compared the physiological similarities between laboring women and athletes, eg, increased stroke volume and cardiac output and

EATING OR DRINKING DURING LABOR

161

delayed gastric emptying. Whatever the validity of these comparisons, the nutritional needs of the mother in labor have not been established, whereas the physiology of exercise is well researched. Unfortunately, despite the rather unsatisfactory data, anesthetists are now frequently asked to provide a risk/benefit analysis of allowing mothers to consume a light diet during labor. The anesthetist who decides to allow this should consider the factors influencing the emptying of solid and semisolid food from the stomach. These include: volume and pH of the ingested meal, fat content of the meal, temperature of the meal, and osmotic pressure. The rate of emptying of the three major food components--carbohydrate, protein, and fat--is regulated so that calories are delivered to the duodenum at a constant rate, suggesting that foods with a relatively high fat content would not be suitable during labor. Sodium chloride 0.9%, a 200 mmol/L -1 isotonic solution, is rapidly emptied from the stomach, whereas solutions of greater (sweet drinks) or lesser osmolality remain in the stomach for longer. Most athletes consume isotonic drinks while exercising, and, in theory, such drinks would be suitable for the mother in labor in that they provide a source of calories and should be rapidly emptied from the stomach and absorbed by the gastrointestinal tract. 31'3a A recent study by Scrutton et a133 aimed to determine whether allowing women in labor to eat a light diet would alter their metabolic profile, influence the outcome of labor, and/or increase the residual gastric volume with consequent risk of pulmonary aspiration. Mothers were randomized to receive a light diet (n = 48) or water only (n = 46) during labor; all were at 37 weeks gestation or greater and had a single fetus with a cephalic presentation. Mothers

requesting intramuscular meperidine were excluded whereas mothers who required epidural analgesia received an infusion of 0.0625%-0.1% bupivacaine with fentanyl 2/~g/mL. Mothers in the eating group were offered a low-residue diet (crackers, cereal, bread, low-fat cheese) throughout labor. Plasma /3-hydroxybutyrate, nonesterified fatty acids, glucose, insulin, and lactate were measured in early labor and again at the end of the first stage. Residual gastric volumes were estimated during the first hour after delivery using a highresolution ultrasound scanner, and the cross-sectional area of the gastric antrum was compared in the two groups. Parameters of labor outcome also were evaluated. There was no difference between the two groups in any of the baseline metabolic measurements. However, at the end of labor plasma/3-hydroxybutyrate and nonesterified fatty acids were significantly higher and plasma glucose and insulin significantly lower in the fasted group (Table 1). Despite the differences in metabolic parameters between the two groups, the duration of labor, use of oxytocin, and mode of delivery were similar. Gastric antral cross-sectional areas measured within 1 hour of delivery were significantly higher in the eating group (Table 2). The mothers who had eaten during labor were also twice as likely to vomit at or around delivery than those in the fasted group, and the volume of vomit measured was significantly larger (Table 2). The residual gastric volumes as estimated in this study were increased in the mothers who consumed a light diet, and the volumes vomited by these mothers support the ultrasonic findings. Eating results in a large increase in the rate of secretion, particularly in the first hour after the consumption of the food, and this contributed to the

Table 1. Plasma Values of Metabolites Measured at the end of the First Stage of Labor*

Metabolite

Eating Mean (SE)

StarvedMean (SE)

Estimateof Difference

95% CI of Difference

P

/3-hydroxybutyrate (mmol/L 1) Non-esterified fatty acids (mmol/L -1) Glucose (mmol/L -1) Insulin (/~mol/L -1) Lactate (mmol/L- 1)

0.20 (.03) 0.85 (0.05) 5.20 (0.14) 23.6 (5.8) 1.89(0.17)

0.58 (.08) 1.20 (0.05) 4.58 (0.15) 9.0 (0.6) 1.58(0.12)

0.38 0.35 0.62 15.6 0.29

0.21-0.55 0.22-0.48 0.22-1.01 2.90-28.30 -0.71-0.12

2.3 x 10 -5 9.3 • 10 -z .003 .017 .167

Abbreviation: CI, confidence interval. * Estimates adjusted for baseline and CIs use robust standard errors. Reprinted with permissionY

162

O'SULLIVAN, KUBLI, A N D SCRUTTON Table 2. Gastric Antral Cross-Sectional Area and Incidence and Volume of Vomiting

Eating No. gastric antra successfullyvisualized Mean (SD) gastric antral cross-sectionalarea (cm2) No. vomiting Mean (SE) vomited (mL) (of those vomiting)

26 (74%) 6.35 17 (38%) 309 (173)

S t a r v e d Estimateof Difference 24 (80%) 4.50 8 (19%) 104 (83)

-1.85 19% 205

95% CI

P

-0.81-2.88* 0.8-38 99-311"

-.001 0.046 t .001

Abbreviation: CI, confidence interval. * CIs calculated using robust SEs. t X2 test. Reprinted with permission.33

increase in the gastric volumes seen in this study. 34 Mothers also complained that vomiting, particularly in the second stage of labor, was very unpleasant. In fact, the mothers with the greatest desire to eat were those who had good pain relief, suggesting that the physiological response to labor (or perhaps to pain) is to avoid solid food. This meant that mothers with effective epidural analgesia were eating solid food during both the first and second stages of labor! It could be argued that the effect of epidural fentanyl, in doses in excess of 100 /xg~, on the rate of gastric emptying during labor means that eating is contraindicated even if these mothers are those with the greatest desire to eat. In view of the large volumes vomited by the mothers who had eaten during labor, it could be argued that they were at increased risk of pulmonary aspiration should they have required emergency general anesthesia. This indicates that restricting the intake of food during labor may have contributed to the decrease in maternal mortality from Mendelson's Syndrome. Because only a relatively small calorie intake was required to prevent the development of ketosis, isotonic drinks, which are rapidly emptied from the stomach and absorbed by the gastrointestinal tract, might be a suitable alternative to solid food during labor. A study evaluating the use of isotonic drinks during labor has recently been completed, and preliminary results suggest their use prevents the development of ketosis without increasing intragastric volume. Observations of mothers during labor suggest that most do not crave food at all. In addition, a substantial number of women feel nauseous or indeed vomit during labor, which contributes to their disinterest in food. Eating during labor has perhaps become a battle between the medical

(high-tech) and nonmedical (low-tech) practitioners who attend the mother in childbirth. The nutritional needs of the laboring mother are unknown and possibly complex, and obstetric and anesthetic interventions are too crude and arguably too medically and legally oriented to allow us to evaluate what is best for the mother. Although there are no data to support the North Bronx retrospective survey, much larger randomized studies are required to assess the impact of feeding in labor on obstetric outcome. The labors of mothers in many obstetric units are dictated by the principles of "active management," thereby possibly limiting their duration. The current shift away from the active management of labor 35 could increase the impact of fasting/feeding policies. Until further studies evaluating the impact of feeding during labor on obstetric outcome have been completed, anesthetists should be cautious about mothers' consumption of solid food during labor. However, it might be reasonable to allow isotonic drinks to relieve thirst, particularly in view of their ability to prevent the metabolic consequences of fasting during labor. REFERENCES l. Mendelson CL: The aspiration of stomach contents into the lungs during obstetric anesthesia. Am J Obstet Gyneco152:191206, 1946 2. Reports on Confidential Enquiries into Maternal Deaths in United Kingdom 1994-1996. London, England, 1998, HMSO 3. Reports on Confidential Enquiries into Maternal Deaths in England and Wales/United Kingdom 1985-1993. London, England, 1991, 1994, 1996, HMSO 4. Reports on Confidential Enquiries into Maternal Deaths in England and Wales 1952-1954. London, England, 1955, HMSO 5. Bainbridge ET, Temple JG, Nicholas SP, et al: Symptomatic gastro-oesophageal reflux in pregnancy: A comparative study of white Europeans and Asians in Birmingham. Br J Clin Pract 37:53-57, 1983

EATING OR DRINKING DURING LABOR 6. Hey VMF, Cowley DJ, Ganguli PC, et al: Gastro-oesophageal reflux in late pregnancy. Anaesthesia 32:372-377, 1977 7. Murray FA, Erskine JP, Fielding J: Gastric secretion in pregnancy. Br J Obstet Gynaecol 64:373-381, 1957 8. Hirsheimer A, January DA, Daversa JJ: An x-ray study of gastric function during labor. Am J Obstet Gynecol 36:671-673, 1938 9. La Salvia LA, Steffen EA: Delayed gastric emptying time in labor. Am J Obstet Gynecol 59:1075-1081, 1950 10. Davison JS, Davison MC, Hay DM: Gastric emptying time in late pregnancy and labour. Br J Obstet Gynaecol 77: 37-41, 1970 11. Carp H, Jayaram A, Stoll M: Ultrasound examination of the stomach contents of parturieuts. Anesth Analg 74:683-687, 1992 12. O'Sullivan GM, Sutton AJ, Thompson SA, et al: Noninvasive measurement of gastric emptying in obstetric patients. Anesth Analg 66:505-509, 1987 13. Nimmo WS, Wilson J, Prescott LF: Narcotic analgesics and delayed gastric emptying during labour. Lancet 1:890-893, 1975 14. Nimmo WS, Wilson J, Prescott LF: Further studies of gastric emptying during labour. Anaesthesia 32:100-101, 1977 15. Volans GiN: Absorption of effervescent aspirin during migraine. Br Med J 4:265-269, 1974 16. Ewah B, Yau K, King M, et al: Effect of epidural opioids on gastric emptying in labour. Int J Obstet Anesth 2:125-128, 1993 17. Geddes SM, Thorburn J, Logan RW: Gastric emptying following Caesarean section and the effect of epidural fentanyl. Anaesthesia 46:1016-1018, 1991 18. Porter JS, Bonello E, Reynolds F: The influence of epidural administration of fentanyl infusion on gastric emptying in labour. Anaesthesia 52:1151-1156, 1997 19. Heading RC, Nimmo J, Prescott LF, et al: The dependence of paracetamol absorption on the rate of gastric emptying. Br J Pharmacol 47:415-421, 1973 20. Tarno-Mordi WO, Shaw JCL, Lin D, et al: Iatrogenic hyponatraemia of the newborn due to maternal fluid overload: A prospective study. Br Med J 283:639-642, 1981

163 21. Feeney JG: Water intoxication and oxytocin. Br Med J 284:243, 1982 22. Metzger BE, Vileisis RA, Ramikar V, et al: "Accelerated starvation" and the skipped breakfast in late normal pregnancy. Lancet 1:588-592, 1982 23. Dumoulin JG, Foulkes JEB: Ketonuria during labour. Br J Obstet Gynaecol 91:97-98, 1984 24. Bencini FX, Symonds EM: Ketone bodies in fetal and maternal blood during parturition. Aust N Z J Obstet Gynaecol 12:176-178, 1972 25. Lawrence GF, Brown VA, Parsons RJ, et al: Fetomaternal consequences of high-dose glucose infusion during labour. Br J Obstet Gynaecol 89:27-32, 1982 26. Lind T: Fluid balance during labour: A review. Royal Soc Med 76:870-5, 1983 27. Changing Childbirth: Report of the Expert Maternity Group. London, England: HMSO, 1993 28. Simkin P: Stress, pain and catecholamines in labor, part 2: Stress associated with childbearing events: A pilot survey of new mothers. Birth 13:234-240, 1986 29. Ludka L: Fasting during labour. In Proceedings of International Confederation of Midwives 2P t Congress in The Hague, 1987 30. Haire DB, Elsberry CC: Maternity care and outcomes in a high-risk service: The North Central Bronx Hospital experience. Birth 18:1, 1991 31. Sole CC, Noakes TD: Faster emptying for glucosepolymer and fructose solutions than for glucose in humans. Eur J Appl Physiol 58:605, 1989 32. Vist GE, Maughn RJ: Gastric emptying of ingested solutions in man: Effect of beverage concentration. Med Sci Sports Exerc 26:1269, 1994 33. Scrntton MJL, Metcalfe GA, Lowy C, et al: Eating in labour: A randomised controlled trial assessing the risks and benefits. Anaesthesia 54:329-334, 1999 34. Malagelada JR, Longstreth GF, Summerskill WHJ, et al: Measurement of gastric function during digestion of ordinary solid meals in man. Gastroenterology 70:203-210, 1976 35. Olah KS, Gee H: The active mismanagement of labour. Br J Obstet Gynaecol 103:729-731, 1996