Maternal use of thyroid hormones in pregnancy and neonatal outcome.
OBJECTIVE
To describe neonatal outcome including the presence of congenital malformations in infants born to women substituted with thyroid hormones, and the maternal characteristics of these women.


METHODS
Register study based on prospectively collected data in relation to delivery.


METHODS
Swedish Health Registers.


METHODS
All pregnant women (n=848,468) and all infants born (n=861,989) in Sweden from 1 July 1995 to 31 December 2004.


METHODS
Women who reported the use of thyroid hormones in early pregnancy or obtained a prescription for thyroid hormones later in pregnancy (n=9,866), as well as their infants (n=10,055) were identified from the Swedish Medical Birth Register. The reference population consisted of all women giving birth and their offspring during the same time interval.


METHODS
Neonatal outcome, malformations and maternal characteristics. Data were analyzed with adjustments for identified confounders.


RESULTS
Women using thyroxine had an increased rate of pre-eclampsia, diabetes (pre-existing or gestational), cesarean sections and inductions of labour compared to women in the reference population. The risk for preterm birth was marginally increased (OR 1.13, 95% CI 1.03-1.25). Neonatal thyroid disease was found in eight infants (seven with thyreotoxicosis and one unspecified), the expected number was 0.2. No further anomalies in neonatal diagnoses were found. A small but statistically significant risk for congenital malformations (OR =1.14, 95% CI 1.05-1.26) was found.


CONCLUSIONS
Women on thyroid substitution during pregnancy had an increased risk for some pregnancy complications, but their infants were only slightly affected.
Department of Medicine, Karolinska Institutet, Clinical Pharmacology Unit, Karolinska University Hospital, Stockholm, Solna, Sweden. birgitta.norstedt-wikner@karolinska.se
Birgitta Norstedt
BN
Wikner
Lottie Skjöldebrand
LS
Sparre
Carl-Olav
CO
Stiller
Bengt
B
Källén
Charlotte
C
Asker
D000328:Adult; D000013:Congenital Abnormalities / Q000209:etiology; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000188:drug therapy*; D007231:Infant, Newborn; D007232:Infant, Newborn, Diseases / Q000209:etiology; D008875:Middle Aged; D011247:Pregnancy; D011248:Pregnancy Complications / Q000188:drug therapy* / Q000209:etiology; D011256:Pregnancy Outcome; D012042:Registries; D013963:Thyroid Hormones / Q000009:adverse effects* / Q000627:therapeutic use
D013963:Thyroid Hormones