Birthweight percentiles by gestational age for births following assisted reproductive technology in Australia and New Zealand, 2002-2010.

STUDY QUESTION: What is the standard of birthweight for gestational age for babies following assisted reproductive technology (ART) treatment?

SUMMARY ANSWER: Birthweight for gestational age percentile charts were developed for singleton births following ART treatment using population-based data.

WHAT IS KNOWN ALREADY: Small for gestational age (SGA) and large for gestational age (LGA) births are at increased risks of perinatal morbidity and mortality. A birthweight percentile chart allows the detection of neonates at high risk, and can help inform the need for special care if required.

STUDY DESIGN, SIZE, DURATION: This population study used data from the Australian and New Zealand Assisted Reproduction Database (ANZARD) for 72 694 live born singletons following ART treatment between January 2002 and December 2010 in Australia and New Zealand.

PARTICIPANTS/MATERIALS, SETTING, METHODS: A total of 69 315 births (35 580 males and 33 735 females) following ART treatment were analysed for the birthweight percentile. Exact percentiles of birthweight in grams were calculated for each gestational week between Week 25 and 42 for fresh and thaw cycles by infant sex. Univariate analysis was used to determine the exact birthweight percentile values. Student t-test was used to examine the mean birthweight difference between male and female infants, between single embryo transfer (SET) and double embryo transfer (DET) and between fresh and thaw cycles.

MAIN RESULTS AND THE ROLE OF CHANCE: Preterm births (birth before 37 completed weeks of gestation) and low birthweight (<2500 g) were reported for 9.7 and 7.0% of live born singletons following ART treatment. The mean birthweight was 3280 g for live born singletons following fresh cycles (3338 g for male infants and 3217 for female infants) and 3413 g for live born singletons following thaw cycles (3475 g for male infants and 3349 for female infants). The proportion of SGA for male ART births following thaw cycles at 35-41 weeks gestation was significantly lower than for the Australian general population, ranging from 3.8% (95% confidence interval (CI): 1.3%, 6.2%) at 35 weeks gestation to 7.9% (95% CI: 6.3%, 9.5%) at 41 weeks gestation. The proportion of LGA for male ART births following thaw cycles was significantly higher than for the Australian general population between 33 weeks (17.1%, 95% CI: 8.9%, 25.2%) and 41 weeks (14.4%, 95% CI: 12.3%, 16.5%). A similar trend was shown for female infants following thaw cycles. The live born singletons following SET were, on average, 45 g heavier than live born singletons following DET (P< 0.001). Overall, SGA was reported for 8.9% (95% CI: 8.6%, 9.1%) of live born singletons following SET and for 9.9% (95% CI: 9.5%, 10.3%) of live born singletons following DET.

LIMITATIONS, REASONS FOR CAUTION: Birthweight percentile charts do not represent fetal growth standards but only the weight of live born infants at birth.

WIDER IMPLICATIONS OF THE FINDINGS: The comparison of birthweight percentile charts for ART births and general population births provide evidence that the proportion of SGA births following ART treatment was comparable to the general population for SET fresh cycles and significantly lower for thaw cycles. Both fresh and thaw cycles showed better outcomes for singleton births following SET compared with DET. Policies to promote single embryo transfer should be considered in order to minimize the adverse perinatal outcomes associated with ART treatment.

STUDY FUNDING/COMPETING INTERESTS: No specific funding was obtained. The authors have no conflicts of interest to declare.