Maternal thyroid dysfunction in pregnancy. Prevalence and effect on perinatal outcome.

Thesis event information

Date and time of the thesis defence

Place of the thesis defence

Oulu University Hospital, lecture hall 4. Remote access:

Topic of the dissertation

Maternal thyroid dysfunction in pregnancy. Prevalence and effect on perinatal outcome.

Doctoral candidate

M.D. Suvi Turunen

Faculty and unit

University of Oulu Graduate School, Faculty of Medicine, Oulu University Hospital, Obstetrics and Gynecology

Subject of study



Docent Eeva Ekholm, Turku University Hospital


Docent Eila Suvanto, Oulu University Hospital

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Maternal thyroid dysfunction in pregnancy; prevalence and effect on perinatal outcome

Maternal thyroid dysfunction during pregnancy is common and has been associated with pregnancy complications and adverse perinatal outcomes. The aim of this epidemiological study was to investigate the associations between maternal thyroid disease and adverse pregnancy and perinatal outcomes as well as the trends in the use of thyroid medication during pregnancy.

The source population for this study was drawn from the Finnish Medical Birth Register (MBR) between 2004 and 2013/2016 and was supplemented with data from the Prescription Register, the Special Refund Entitlement Register, the Care Register for Health Care (HILMO), and the Register on Congenital Malformations. Hypothyroid and hyperthyroid mothers with and without thyroid medication were identified from the MBR and compared to mothers without any thyroid disease.

The overall prevalence of hypothyroidism in pregnancy was 3%. Most hypothyroid women used levothyroxine during pregnancy, and the rate of levothyroxine use during pregnancy increased more than five-fold during the study period. Maternal hypothyroidism was associated with increased risk of several adverse pregnancy outcomes, such as gestational hypertensive disorders, gestational diabetes, and preterm births. The risks of hypertensive disorders and preterm births were lower in women who used levothyroxine throughout pregnancy.

The prevalence of hyperthyroidism in pregnancy was 0.4%. Women with active hyperthyroidism, as well as those with a history of hyperthyroidism, were at risk of developing pregnancy complications, such as gestational hypertensive disorders. They also had an increased risk of caesarean section and preterm birth. In addition, newborns of mothers with thyroid disease had a higher risk of neonatal intensive care unit treatment.

In conclusion, both maternal hypothyroidism and hyperthyroidism were associated with adverse pregnancy and perinatal outcomes. The observed increase in the rate of thyroid hormone use suggests that awareness of the effects of thyroid disorders on pregnancy outcome has increased and that the threshold to treat thyroid dysfunction has declined in Finland.
Last updated: 1.3.2023