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Maternal thyroid function in multifetal pregnancies before and after fetal reduction
O Ogueh1, A P Hawkins, A Abbas
1Section of Obstetrics and Gynaecology, Imperial College School of Medicine, Chelsea and Westminster Hospital, 369 Fulham Road, London SW10 9NH, UK.
The Journal of Endocrinology
|December 23, 1999
Summary
Maternal thyroid function, specifically free thyroxine (fT4) levels, is elevated in multifetal pregnancies. These levels decrease after fetal reduction but remain higher than in twin pregnancies, suggesting a delayed response to human chorionic gonadotrophin (hCG) or a fetal factor influence.
Area of Science:
- Reproductive Endocrinology
- Maternal-Fetal Medicine
- Thyroid Physiology
Background:
- Multifetal pregnancies are associated with significant physiological changes in the mother.
- Thyroid hormone levels, including thyroid stimulating hormone (TSH) and free thyroxine (fT4), are known to fluctuate during pregnancy.
- Human chorionic gonadotrophin (hCG) levels are elevated in pregnancy and can influence maternal thyroid function.
Purpose of the Study:
- To investigate maternal thyroid function in multifetal pregnancies.
- To monitor circulating concentrations of TSH, fT4, and hCG before and after selective fetal reduction.
- To explore the relationship between fetal load, hCG, and maternal thyroid hormone levels.
Main Methods:
- Study included singleton, twin, and multifetal pregnancies (n=39) undergoing selective fetal reduction to twins.
- Blood samples were collected at 10-12 weeks gestation (pre-reduction) and 4 and 8 weeks post-reduction.
- Circulating concentrations of TSH, fT4, and hCG were measured using standard assays.
Main Results:
- Pre-reduction, multifetal pregnancies had significantly higher fT4 levels compared to singleton and twin pregnancies.
- fT4 levels were significantly related to the number of fetuses but not to hCG concentrations before reduction.
- Post-reduction, fT4 levels decreased but remained significantly elevated at 4 and 8 weeks compared to control twin pregnancies, lagging behind hCG normalization.
Conclusions:
- Maternal thyroid function, specifically fT4, is altered in multifetal pregnancies, influenced by the number of fetuses.
- The observed pattern suggests a delayed thyroid response to decreasing hCG levels after fetal reduction.
- An additional fetal factor, beyond hCG, may also regulate maternal thyroid function in multifetal pregnancies.