Hormone therapy before frozen embryo transfer is tied to larger babies but not to differences in early childhood IQ
Children conceived through frozen embryo transfers using hormone therapy show similar early childhood intelligence scores to those conceived via natural cycles, according to a new study, despite a higher rate of unusually large babies.
A recent study published in Reproductive Biology and Endocrinology suggests that hormone replacement therapy used in preparing the uterus for frozen embryo transfer does not significantly impact early childhood intelligence, but it does lead to a higher proportion of unusually large infants and more neonatal intensive care admissions.
Assisted reproductive technology offers medical procedures to help people achieve pregnancy, with frozen embryo transfer becoming more common due to advancements in freezing techniques. During this procedure, an embryo created in a lab is frozen, thawed later, and then inserted into the mother's uterus. Preparing the uterine lining to accommodate the embryo is crucial, requiring synchronization with the woman's menstrual cycle.
Women with regular periods typically undergo one of two methods: the natural cycle method, which relies on the woman's hormonal cycle, or hormone replacement therapy, which involves providing external hormones, mainly estrogen and progesterone, to artificially build up the uterine lining. The hormone replacement therapy method, however, bypasses natural ovulation and instead uses medication to artificially elevate uterine lining thickness in preparation for the embryo.
Researchers led by Xiaomeng Shi, Minyue Tang, and Yimin Zhu from Zhejiang University investigated whether this hormone therapy affects children's intelligence. They analyzed intelligence assessments of children aged three to six, an age range free from puberty's influence, to provide guidance for parents choosing embryo transfer protocols.
Out of 1,538 families recruited, 434 children conceived using the natural cycle method and 356 conceived using hormone replacement therapy met the criteria. The study found no significant differences in verbal intelligence, performance intelligence, or full-scale IQ between the two groups, with the hormone group scoring about two points lower in full-scale IQ, though the difference was not statistically significant.
No significant differences in vocabulary subtest scores or intellectual disability rates (IQ below 80) were observed. The researchers also found no sex or fertilization method-based IQ differences, though hormone therapy groups had higher estrogen levels shortly before transfer, potentially explaining the slightly better vocabulary performance.
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