Effects of timing of conception on birth weight and preterm delivery of natural family planning users
Objective: Various birth defects and untoward perinatal outcomes have been claimed to be associated with pregnancies conceived by gametes aged in vivo before fertilization. Thus, these outcomes were systematically assessed in pregnancies occurring in natural family planning (NFP) users. Our international multicenter cohort study of NFP pregnancies (n = 877) is by far the largest systematic study designed to assess pregnancy outcome and is of sufficient power to allow us to address the concern of low birth weight (< 2500 g) and preterm delivery (< 37 weeks gestation).
Study design: In addition to gathering baseline medical data, evaluation was performed at 16 weeks, 32 weeks and at term. Data were collected in a systematic cohort fashion, verified by the five collaborating international recruiting centers, and analyzed by investigators in the US. Most recruiting center principal investigators are obstetrician-gynecologists and, if not, have integral relationships with such specialists. Standard criteria could thus be applied within and among centers. In our cohort, birth weight was recorded accurately at delivery. Almost all of the deliveries occurred in hospitals; thus, data should be quite reliable. Neonatal examination for anomalies was usually conducted immediately after delivery, when birth weight was recorded.
Results: Analysis of risk factors for low birth weight and pretern delivery showed that this population had a low risk profile. Low birth weight infants (< 2500 g) and preterm deliveries were increased among women with a history of either prior low birth weight or preeclampsia in the index pregnancy. However, mean birth weight was unaffected by the timing of conception vis à vis ovulation or pregnancy history. Mean birh weight for the 877 singleton NFP pregnancies was 3349.6 g. The risk of preterm delivery was increased among older women who drank alcohol, but there were no significant effects of timing of conception vis à vis ovulation on preterm delivery. Results held when analysis was stratified according to whether NFP was being used for contraception or to achieve pregnancy.
Conclusions: Our data do not appear to show striking differences between 877 NFP pregnancies and the general obstetric population. The timing of conception vis à vis ovulation does not exert significant effects on the birth weight or preterm delivery of resulting pregnancies, a reassuring finding for NFP users.
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- 1.Gray RH, Simpson JL, Kambic RT et al. Timing of conception and the risk of spontaneous abortion among pregnancies occurring during use of natural family planning. Am J Obstet Gynecol. 1995; 172: 1567–72.Google Scholar
- 2.Simpson JL, Gray RH, Queenan JT et al. Pregnancy outcome associated with natural family planning (NFP): scienti¢c basis and experimental design for an international cohort study. Adv Contracept. 1988; 4: 247–64.Google Scholar
- 3.Simpson JL, Gray RH, Queenan JT et al. Fetal outcome among pregnancies in natural family planning acceptors: an international cohort study. Am J Obstet Gynecol. 1991; 165(suppl): 1981–2.Google Scholar
- 4.Bitto A, Gray RH, Simpson JL et al. A prospective study of pregnancy outcomes among planned and unplanned pregnancies in natural family planning users. Am J Pub Health. 1997. [In press].Google Scholar
- 5.Kambic R, Gray RH. Interobserver variation in estimation of day of conception intercourse using selected natural family planning charts. Fertil Steril. 1989; 51(3): 430–4.Google Scholar
- 6.World Health Organization. Manual of the International Statistical Classi¢cation of Diseases, Injuries and Causes of Death, 9th revision.Volumes 1 and 2, World Health Organization, Geneva, 1975.Google Scholar
- 7.Fleiss JL. Statistical Methods for Rates and Proportions. New York: John Wiley and Sons, 1981.Google Scholar
- 8.Armitage P, Berry G. Statistical Methods in Medical Research. Oxford: Blackwell Scienti¢c Publica-tions, 1987.Google Scholar
- 9.Hosmer DW, Lemeshow S. Applied Logistic Reactions. New York: John Wiley and Sons, 1989.Google Scholar
- 10.Gray RH, Simpson JL, Bitto A et al. Sex ratio associated with timing of conception and length of the follicular phase in planned and unplanned pregnancies during use of natural family planning. [Submitted].Google Scholar
- 11.German J. Mongolism, delayed fertilization, and human sexual behavior. Nature. 1968; 217: 516–8.Google Scholar