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Accepted Preprint first posted on 9 March 2009 as Manuscript EJE-08-0953
N.Benhadi 1
Higher maternal TSH levels in pregnancy are associated with
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increased risk for miscarriage, fetal or neonatal death
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N. Benhadi1, W.M. Wiersinga1, J.B. Reitsma2, T.G.M. Vrijkotte3, G.J. Bonsel3.
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of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam.
Departement of Endocrinology and Metabolism, Academic Medical centre of the University
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Departement of Clinical Epidemiology, Biostatistics and Bioinformatics, Academic Medical
Centre of the University of Amsterdam, Meibergdreef 9, 1105 AZ, Amsterdam
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Meibergdreef 9, 1105 AZ, Amsterdam.
Departement of Social Science, Academic Medical Centre of the University of Amsterdam,
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Corresponding author:
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N. Benhadi, Departement of Endocrinology and Metabolism, Academic Medical Centre of the
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University of Amsterdam, Meibergdreef 9, 1105 AZ Amsterdam, The Netherlands.
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Telephone: +31 (0)20 5666964, Fax: +31 (0)20 6917682, Email:
[email protected].
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Running title: Increasing TSH associated with higher risk for child loss.
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Word count: 2,675
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1 Copyright © 2009 European Society of Endocrinology.
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N.Benhadi 1
Abstract
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Background: To examine the relationship between maternal Thyroid Stimulating Hormones
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(TSH) and free Thyroxine (T4) concentrations in early pregnancy and the risk of miscarriage,
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fetal or neonatal death.
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Method: Cohort study of 2497 Dutch women. TSH, free T4 and Thyroid Peroxidase
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Antibodies (TPO-Ab) concentrations were determined at first booking. Child Loss was
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operationalised as miscarriage, fetal or neonatal death. Women with overt thyroid dysfunction
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were excluded.
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Results: 27 cases of child loss were observed. The mean TSH and free T4 level in the women
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with child loss was 1.48 mU/L and 9.82 pmol/L compared to 1.11 mU/L and 9.58 pmol/l in
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women without child loss. The incidence of child loss increased by 60% (OR= 1.60
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(95%CI:1.04-2.47)) for every doubling in TSH concentration. This association remained after
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adjustment for smoking, age, parity, DM, Hypertension, previous preterm deliveries and
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previous preterm stillbirth/miscarriage (AOR= 1.80 (95%CI: 1.07- 3.03)). This was not true
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for FT4 concentrations (OR= 1.41 (95%CI: 0.21- 9.40); P=0.724).
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Conclusion: In a cohort of pregnant women without overt thyroid dysfunction, the risk of
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child loss increased with higher levels of maternal TSH, Maternal free T4 concentrations and
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child loss was not associated.
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Key Words: TSH, pregnancy outcome, thyroid function, risk.
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N.Benhadi 1 2
Introduction Thyroid hormones are vital for the development of the brain both during fetal and
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early postnatal life. Impaired maternal thyroid hormone availability may induce irreversible
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brain damage with consequent neurological abnormalities (1-8). So far, only the effects of
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subclinical and overt hypo- and hyperthyroidism on pregnancy outcome have been studied.
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Overt maternal hypothyroidism in the first trimester is associated with preterm delivery and
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fetal death (9). Haddow JE and colleagues (1999) reported that children of women whose
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thyroid stimulating hormone (TSH) levels were increased during midterm of pregnancy had a
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slight but significant reduction in intelligence quotient score between 7 and 9 years of age if
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compared with infants of euthyroid women (10). Allan WC, Haddwon JE et al (2002) showed
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that TSH levels above 6 mU/L are significantly associated with a higher frequency of still
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birth (11). Women with resistance to thyrod hormone (RTH), (high free T4 thyroxine (T4)
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levels accompanied with normal or slightly elevated TSH levels) have a higher rate of
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miscarriage (12). In a study of Casey BM, Dashe JS et al. (2007) there was no significant
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adverse effects on perinatal outcome in women with maternal hypothyroxinemia (low free T4
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levels accompanied with normal TSH levels) in the first half of their pregnancy (13).
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From the evidence in cases with overt hypo- or hyperthyroidism we would expect both
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low and high TSH and free T4 to be associated with miscarriage, fetal or neonatal death (child
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loss). The purpose of the present study was to examine the association between maternal
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levels of TSH, free T4, thyroid peroxidase antibodies (TPO-Ab) measured in pregnancy and
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subsequent child loss, excluding women with known thyroid disease or overt hypo- or
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hyperthyroidism.
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The study was carried out using data from native Dutch pregnant women without
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known or clinical thyroid disease, who participated in a large population-based cohort study
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(ABCD-study, Amsterdam 2003-2004). Other ethnic groups participating in this study were
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N.Benhadi 1
excluded from the present analysis, because of significant difference in serum TSH and in
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pregnancy outcome that exist between the various ethnic groups (14).
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Methods
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Subjects
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Our study was nested within a prospective cohort study of pregnant women from the
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Amsterdam Born Children and their Development (ABCD) study (14). The main objective of
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the ABCD study is to examine differences in pregnancy outcome, focussing on ethnic
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background, maternal lifestyle factors and psychosocial conditions on the outcome of the
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pregnancy and the baby’s health. The ABCD study is a collaborative effort of the Municipal
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Health Services (GGD) and all hospitals and midwife practices in Amsterdam, the
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Netherlands. All pregnant women living in the city of Amsterdam were invited to participate
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at their first visit to an obstetric caregiver between January 2003 and March 2004. Of 12,377
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pregnant women invited, 8,266 women agreed to participate (response rate 67%). These
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women filled out a questionnaire including questions about social demographic characteristics
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and ethnic background. 4,267 women gave additional informed consent for blood collection
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during their first visit which took place on average in the 13th week of gestation. The study
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protocol was approved by the medical ethnical committees of all Amsterdam hospitals and the
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Registration Committee of Amsterdam, and participants gave their written informed consent.
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N.Benhadi 1 2
Baseline characteristics All pregnant women received a pregnancy questionnaire at their home address two
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weeks after their first antenatal visit. The questionnaire contained demographic, health
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history, medication and lifestyle questions, all from existing validated sources. All
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approached women were asked to return the pregnancy questionnaire by prepaid mail. A
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written reminder was sent two weeks after the initial mailing.
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Smoking status during pregnancy, parity, age and BMI were determined from the self
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reported information. In this study we recoded smoking as a dichotomous question for current
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smoking (yes/no), regardless the amount of cigarettes smoked daily. Parity was recoded in a
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categorical variable 90, 1 and 2+). BMI was based on the length and weight of the mother
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before pregnancy. Alcohol was not included in the analysis of our study in view of the very
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low levels of alcohol use among the Dutch pregnant women in our study population.
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Hypertension (no, pre-existent and gestational hypertension) and diabetes mellitus (nu,
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pre-existent and gestational diabetes) were based on self-reported information from the
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questionnaire and completed by information from the national obstetric registry (Perinatal
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Registration centre of the Netherlands) (14). This registry was linked to the ABCD data by
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probabilistic record linkage (15). These data were gathered by a trained health care provider.
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We also recorded women who had a preterm delivery in previous pregnancies and
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previous miscarriage or stillbirth. In our stillbirth/miscarriage variable we included intra-
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uterine deaths as well. All these data were based on the information from trained health care
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providers from the national obstetric registry (Perinatal Registration centre of the
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Netherlands) (14).Validation has shown close to perfect results for these variables.
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N.Benhadi 1
Assays
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For our study serum TSH, free Thyroxine (FT4) and antibodies against thyroid
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peroxidase (TPO-Ab) were assayed. TSH (reference range, 0.34-5.60 mU/L) and FT4
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concentration (reference range, 7.5- 21.1 pmol/L) were measured in serum by means of
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Access immunoanalyzer of Beckman Coultier, Inc. The inter-assay variation for TSH was
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5.0% and for FT4 the inter-assay variation was 3.1-5.0%. Antibodies against Thyroid
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Peroxidase (TPO-Ab) were determined by Elisa ELIZEN TG Ab (E-CK-96), Zentech, Luik,
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Belgium. A TPO-Ab concentration above 80 kU/L was considered as positive. The inter-
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assay variation was 13.4%.
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Overt hyperthyroidism was defined as having a TSH concentration below 0.4 mU/L in
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combination of FT4 concentration above the upper limit of 21.1 pmol/L. Overt
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hypothyroidism was defined as a TSH above the 4.0 mU/L upper limite in combination with a
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FT4 below the lower limit of 7.5pmol/L.
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Outcomes The occurrence of miscarriage, fetal death or neonatal death (child loss( was
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determined from3 overlapping sources; 1) the National Midwife Registry, 2) the National
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Obstetricians Registry and 3) the National Neonatal Registry. Miscarriage was defined as
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death of the fetus occurring before 22 weeks of gestation. Fetal death and neonatal death were
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defined according to existing standards (fetal death: death occurring from 22 weeks of
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gestation until delivery; neonatal death: death from 0-7 days after delivery). Fetal death
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includes stillbirth and intra-uterine deaths in our cohort.
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N.Benhadi 1 2
Statistical Analysis Differences in demographic and clinical characteristics were analyzed in a descriptive
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way. Logistic regression models were built to explore the relationship between TSH, FT4
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concentrations determinants, and the occurrence of miscarriage, fetal death and neonatal death
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in more detail. Restricted also known as natural cubic splines (4knots) were used to examine
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the functional relationship between TSH and free T4 levels in relation to the outcome (17,
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18). Based on these graphical analyses, we used a log transformation (to the power of 2) as
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this clearly improved the linear relationship between TSH and FT4. In addition to the
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univariate analysis we also build a multivariate model containing the following potential
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confounders: current smoker (yes/no), mother’s age (continuous), parity (categorical: 0,1,2+),
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hypertension (no, pre-existent and gestational hypertension), diabetes mellitus (no, pre-
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existent, gestational diabetes), previous preterm deliveries (yes/no), previous
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stillbirth/miscarriages (yes/no) and TPO-Ab presence (yes/no) with TPO-Ab concentration
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below 80kU/L or more as positive. The modelling strategy was the same whether examining
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the relationship between levels of TSH of FT4 with child loss. P-values of less than 0.05 were
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considered statistically significant.
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All statistical analysis was performed using the Statistical package of Social Sciences and Problem Solutions (SPSS version 15.0).
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N.Benhadi 1
Results
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The initial number of native Dutch women within the ABCD cohort giving informed
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consent for blood sampling was 2,684. From this starting cohort we excluded 116 women in
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whom blood sampling occurred after the 27th week of gestation (third trimester). Of the
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remaining, we excluded 29 women who gave birth to twins. We also excluded 18 women
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with over hypo- or hyperthyroidism defined as TSH >5.6 mU/L in combination with FT4< 7.5
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pmol/L and TSH 21.1 pmol/L respectively. Of the
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2,521 women who remained in the study we excluded another 24 with missing TSH values,
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leaving 2,497 women in our analysis (Figure 1).
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Our study population of 2,497 Dutch pregnant women had a mean age of 32.0
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(SD=4.0) years. In 60% of the women this was their first pregnancy and 32% their second.
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9.2% of all women smoked during their pregnancy. There were 129 (5%) women with a TSH
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concentration below 0.34 mU/L and 11 (0.5%) with a TSH value above 5.6 mU/L. A FT4
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concentration below 7.5 pmol/L was seen in 94 women (4%) and there were no women with a
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FT4 value above the 21.1 pmol/L in our study cohort. The overall prevalence of elevated
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TPO-Ab (concentration above > 80kU/L) was 5.8% (146/2497), (see Table I).
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TSH and FT4 levels were negatively correlated (Pearsons’r= -0.375, p
