Maternal thyroid deficiency and pregnancy complications: implications for population screening

Abstract

Objective-To examine the relation between certain pregnancy complications and thyroid stimulating hormone (TSH) measurements in a cohort of pregnant women. Methods-TSH was measured in sera obtained from women during the second trimester as part of routine prenatal care. Information was then collected about vaginal bleeding, premature delivery, low birthweight, abruptio placentae, pregnancy induced hypertension, need for cesarean section, low Apgar scores, and fetal and neonatal death. Results-Among 9403 women with singleton pregnancies, TSH measurements were 6 mU/l or greater in 209 (2.2%). The rate of fetal death was significantly higher in those pregnancies (3.8%) than in the women with TSH less than 6 mU/l (0.9%, odds ratio 4.4, 95% confidence interval 1.9-9.5). Other pregnancy complications did not occur more frequently Conclusion-From the second trimester onward, the major adverse obstetrical outcome associated with raised TSH in the general population is an increased rate of fetal death. If thyroid replacement treatment avoided this problem this would be another reason to consider population screening. (J Med Screen 2000;7:127-130) Keywords: thyroid stimulating hormone; pregnancy; fetal death Although clinically apparent maternal hypothyroidism during pregnancy has long been known to be associated with both maternal and fetal complications, most of the studies documenting those problems have focused on patients in specialty or high risk clinics. The present study assesses the impact of maternal hypothyroidism in a cohort of pregnant women being managed in primary care settings. In 1991, our group reported thyroid stimulating hormone (TSH) measurements in a cohort of 2000 pregnant women whose sera were being obtained for -fetoprotein measurements at 15-18 weeks' gestation as part of routine care. 1 TSH measurements were at, or above, 6 mU/l in 49 of the women (2.4%). In six of these 49 women the thyroxine (T 4 ) and/or free T 4 measurements were suYciently abnormal (more than two standard deviations below the average) for clinical manifestations to be anticipated. It was not possible to gather individual information about health status in this cohort, because all identifiers were removed from the serum samples before the thyroid measurements were performed. Given the frequency of thyroid deficiency identified in this pregnancy population, it was decided that its possible impact on late pregnancy and delivery should be evaluated. To accomplish this, it was necessary to study a second, larger cohort of pregnant women. Materials and methodsThe Foundation for Blood Research oVers prenatal serum screening services for open neural tube defects and Down's syndrome to all primary care prenatal practices in Maine. The testing is generally performed between 15 and 18 weeks' gestation. Approximately two thirds of the women receiving prenatal care in Maine opt for those services.Between July 1990 and June 1992 the order form for the prenatal screening test contained a supplementary consent form, asking women...

11 Hypothyroidism in Pregnancy

“…Raised maternal serum TSH in the second trimester is also associated with an increased rate of fetal death after 16 weeks' gestation [37]. Other studies have found that although women treated for hypothyroidism may have higher rates of preeclampsia and caesarean section than euthyroid women, they are not at any higher risk for adverse outcomes such as fetal anomalies, fetal demise, or preterm birth.…”

“…In a study of women during the second trimester of pregnancy, the prevalence of fetal death was over 4-fold higher in mothers with a TSH concentration ≥6 mIU/L, compared to those whose mothers had a TSH <6 mIU/L (3.8% vs. 0.9%) [37] Untreated hypothyroidism is associated with increased risk of preeclampsia, low birth weight, placental abruption, miscarriage, and perinatal mortality [53,54]. In addition to an increased risk of low birth weight, hypothyroidism (as defined by increased serum TSH) early and late in pregnancy may also increase the rate of caesarean section [55].…”

“…The prevalence of hypothyroidism was similar in the three studies ranging from 2,2 to 2,4%. In the study carried out on 9403 pregnant women, subclinical hypothyroidism was detected in 0,4% of cases [37].…”

“…Anti-thyroid antibodies were found in 18% of Australian women in the late first trimester and were associated with subtle effects on thyroid function [50]. In a prospective population study of 9471 pregnant women in the United States in whom serum TSH was measured during the second trimester, hypothyroidism was diagnosed in 2.2% of the cohort, and autoimmune thyroiditis was present in 55% of women with SCH and more than 80% in women with OH [37].…”

“…Hypothyroidism during pregnancy has been also associated with impaired cognitive development and increased fetal mortality [37].…”