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 ag ed in vivo before fertilization. Thus, these outcomes were systematica lly 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 pr egnancy outcome and is of sufficient power to allow us to address the concern of low birth weight (< 2500 g) and preterm delivery (< 37 week s 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 c ollaborating international recruiting centers, and analyzed by investi gators in the US. Most recruiting center principal investigators are o bstetrician-gynecologists and, if not, have integral relationships wit h 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, d ata should be quite reliable. Neonatal examination for anomalies was u sually conducted immediately after delivery, when birth weight was rec orded. Results: Analysis of risk factors for low birth weight and pret erm delivery showed that this population had a low risk profile. Low b irth weight infants (< 2500 g) and preterm deliveries were increased a mong women with a history of either prior low birth weight or preeclam psia in the index pregnancy. However, mean birth weight was unaffected by the timing of conception vis a vis ovulation or pregnancy history. Mean birth weight for the 877 singleton NFP pregnancies was 3349.6 g. The risk of preterm delivery was increased among older women who dran k alcohol, but there were no significant effects of timing of concepti on vis a vis ovulation on preterm delivery. Results held when analysis was stratified according to whether NFP was being used for contracept ion or to achieve pregnancy. Conclusions: Our data do not appear to sh ow striking differences between 877 NFP pregnancies and the general ob stetric population. The timing of conception vis a vis ovulation does not exert significant effects on the birth weight or preterm delivery of resulting pregnancies, a reassuring finding for NFP users.