Infertility treatment and children's longitudinal growth between birth and 3 years of age.

STUDY QUESTION: Does early childhood growth from birth through to 3 years of age differ by mode of conception? SUMMARY ANSWER: Findings suggest early childhood growth was comparable for children irrespective of infertility treatment, but twins conceived with ovulation induction with or without intrauterine insemination (OI/IUI) were slightly smaller than twins conceived without treatment. WHAT IS KNOWN ALREADY: Although studies have found that babies conceived with infertility treatment are born lighter and earlier than infants conceived without treatment, little research especially for non-assisted reproductive technology (ART) treatments has focused on their continued growth during early childhood. STUDY DESIGN, SIZE, DURATION: Upstate KIDS recruited infants born (2008-2010) to resident upstate New York mothers. Infants were sampled based on birth certificate indication of infertility treatment; specifically, for every singleton conceived by infertility treatment, three singletons without infertility treatment were recruited and matched on region of birth. All multiple births irrespective of treatment were also recruited. Children were prospectively followed, returning questionnaires every 4-6 months until 3 years of age. In total, 3905 singletons, 1129 sets of multiples (96% of whom were twins) enrolled into the study. Analyses included 3440 (88%) singletons (969 conceived with treatment; specifically, 433 with ART and 535 with OI/IUI) and 991 (88%) sets of multiples (439 conceived with treatment; specifically 233 with ART and 206 with OI/IUI) with growth data available. PARTICIPANTS/MATERIALS, SETTING,
METHODS: Mothers reported infertility treatment use at baseline and children's height and weight from pediatric visits. Self-reported use of ART was previously verified by linkage with the US Society for Assisted Reproductive Technology Clinic Outcome Reporting System (SART CORS) database. Mixed linear models with cubic splines accounting for age and age-gender interactions were used to estimate mean differences in growth from birth to 3 years by infertility treatment status and adjusting for maternal age, race, education, private insurance, smoking status during pregnancy, maternal pre-pregnancy and paternal body mass indices (BMI). MAIN RESULTS AND THE ROLE OF CHANCE: Compared with singletons conceived without treatment (n = 2471), singletons conceived by infertility treatment (433 by assisted reproductive technologies (ART), 535 by OI/IUI and 1 unknown specific type) did not differ in growth. Compared with twins not conceived with treatment (n = 1076), twins conceived with OI/IUI (n = 368) weighed slightly less over follow-up (122 g). They were also proportionally smaller for their length (-0.17 weight-for-length z-score units). No differences in mean size over the 3 years were observed for twins conceived by ART, though some evidence of rapid weight gain from birth to 4 months (adjusted OR 1.08; 95% CI: 1.00-1.16) suggestive of catch up growth was observed. LIMITATIONS, REASONS FOR CAUTION: Participants from upstate New York may not be representative of US infants. Although accounted for in statistical analysis, attrition during follow-up may have limited power to detect small differences. WIDER IMPLICATIONS OF THE
FINDINGS: This study is the first to prospectively track the growth of children conceived with and without infertility treatment in the USA, including a substantial number of twins. Our findings are similar to what was previously observed in the ART literature outside of the states. STUDY FUNDING/COMPETING INTERESTS: Supported by the Intramural Research Program of the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD; contracts #HHSN275201200005C, #HHSN267200700019C). Authors have no competing interests to declare. TRIAL REGISTRATION NUMBER: Not applicable. Published by Oxford University Press on behalf of the European Society of Human Reproduction and Embryology 2016. This work is written by (a) US Government employee(s) and is in the public domain in the US.