Association of time to pregnancy and the outcome of pregnancy.

OBJECTIVE

To examine the relationship of subfertility with miscarriage, low birth weight, and preterm delivery.

DESIGN

Comparison of time to pregnancy distributions between pregnancies that had different outcomes. Three comparisons were made: (a) miscarriages with live births; within live births, (b) low birth weight infant (up to 2,500 grams) or not low birth weight; (c) preterm birth (37 weeks or less) or not preterm. Cox regression was used to adjust for covariates.

POPULATION

All first pregnancies were analyzed from the National Child Development Study, a large survey of young adults aged 33 years, which is nationally representative of the British-born population.

MAIN OUTCOME MEASURES

The distribution of the time taken to conceive (time to pregnancy), miscarriage, birth weight, and preterm delivery.

RESULTS

Pregnancies that ended in miscarriage tended to take 23% longer to conceive, after adjustment for the other variables. Pregnancies that resulted in preterm delivery tended to take 15% longer to conceive. There was no statistically significant association with low birth weight.

CONCLUSIONS

Delay in time to conception is a risk factor for poor obstetric outcome, irrespective of medical intervention.