Effect of pregnancy planning and fertility treatment on cognitive outcomes in children at ages 3 and 5: longitudinal cohort study.

OBJECTIVE: To investigate how pregnancy planning, time to conception, and infertility treatment influence cognitive development at ages 3 and 5. DESIGN: Prospective population based cohort study. SETTING: Millennium Cohort Study in the United Kingdom. PARTICIPANTS: 18,818 children recruited at 9 months and followed up at 3 and 5 years. 11,790 singletons with available data on pregnancy, cognitive outcomes, and confounders were included in analyses at age 3 and 12,136 at age 5. Exposure measures Mothers reported whether the pregnancy was planned, and their feelings when first pregnant; those in whom the pregnancy was planned provided time to conception, and details of any assisted reproductive technologies. The population was divided into "unplanned" (unplanned and unhappy), "mistimed" (unplanned but happy), "planned" (planned, time to conception <12 months), "subfertile" (planned, time to conception ≥ 12 months), "induced ovulation" (received clomiphene citrate), and "assisted reproduction" (in vitro fertilisation or intracytoplasmic sperm injection). The "planned" group was the comparison group in all analyses. OUTCOME MEASURES: Three components of the British Ability Scales (BAS II). Naming vocabulary assessed verbal ability at age 3; this test was repeated at age 5 with the picture similarities and pattern construction subscales, which measure non-verbal and spatial abilities. RESULTS: In unadjusted analyses, the scores on all scales in children from unplanned pregnancies were significantly lower than in those from planned pregnancies-for example, the difference in mean verbal ability score at age 3 was -4.8 (95% confidence interval -6.0 to -3.7; P