- Hypothyroidism during
pregnancy is harmful to both the mother and fetus.
hormone replacement is associated with better outcome for both mother and the
- However, treatment can be associated with other
- Current treatment recommendations on
subclinical hypothyroidism in pregnancy may need revision.
recent published study indicates that it is only necessary to treat a pregnant
women with the thyroxine hormone tablets
their TSH concentrations is between 4.1-10 mIU/L and that too during the first
three months of the pregnancy.
is a requirement for a more scientific study on the subject and also the need
to revise the current guidelines on thyroid hormone
treatment in pregnant women with subclinical hypothyroidism.
‘Treatment with thyroid hormone of pregnant women during the first trimester of pregnancy can prevent fetal loss.’
Guidelines on Subclinical Hypothyroidism
to American Thyroid Association guidelines, subclinical hypothyroidism is defined as elevated TSH levels greater
than 2.5 mIU/L
, in the presence of normal thyroid hormone concentrations.
per these guidelines, approximately 15
percent of pregnant women in the US and Europe will have subclinical
, representing a fivefold increase compared to before these
criteria were laid down (2-3%), raising the possibility of over-diagnosis of
exists to indicate the
net benefit of administering thyroid hormone during
pregnancy. Despite this the current
guidelines recommend giving levothyroxine
hormone to treat subclinical hypothyroidism
in pregnant women.
degree to which these recommendations are being followed and implemented at
present is not known.
New Retrospective Study
objective of the retrospective cohort study was to assess
safety versus the risks and efficacy
of administering thyroid hormone to
pregnantwomen with subclinical
retrospective cohort study involved 5405
with untreated subclinical hypothyroidism chosen from a large US
administrative database. The participants were selected based on predetermined
criteria. The study spanned five years
from January 2010 to December 2014
the participants, 843 women
percent) with a mean TSH value of 4.8 mIU/L were treated with thyroid hormone
while 4562 women with a mean TSH concentration of 3.3 mIU/L were not treated.
adverse outcomes assessed included
primarily fetal loss
(miscarriage and stillbirth).
outcomes assessed included preterm labor and delivery, premature rupture of
membranes, gestational diabetes
gestational hypertension, preeclampsia
, placental abruption, and poor fetal growth.
results from the study threw up the following observations -
Following the Study Findings
- Risk of fetal loss was lower in
women treated with thyroxine compared to those who were not
- Treatment with thyroid hormone was associated with
higher incidence of adverse outcomes such as preterm delivery, preeclampsia and
- Thyroid hormone therapy did not
affect the other adverse outcomes assessed such as premature rupture of
membranes, poor fetal growth and placental abruption.
the treated women, the effect of
reducing fetal loss was observed only among women who had pre-treatment TSH
levels of 4.1-10.0 mIU/L, not those with concentrations of 2.5-4.0
physicians and patients are unsure about the overall benefit of thyroid hormone
treatment on maternal and fetal outcome in pregnancy.
on the study findings, it appears reasonable to treat women with TSH
concentrations between 4.1-10 mIU/L with thyroxine replacement. Since the
efficacy of thyroid hormone replacement was not significant in women with TSH levels of 2.5-4 mIU/L
and due to
the occurrence of other adverse outcomes in general, treatment could be withheld
in this group and policy guidelines revised
fact discussions at the 2016 Endocrine Society meeting have suggested increasing the cut-off limit of TSH levels
to 4 mIU/L
in the upcoming American Thyroid Association guidelines.
results from large randomized trials like the TSH study and the pregnancy
complication data from the Controlled Antenatal Thyroid Screening study are
awaited and could possibly provide more scientific rationale for treatment of
pregnancy associated subclinical hypothyroidism.
Limitations of the Study
- This study is the largest national study regarding
thyroid hormone replacement in pregnant women with subclinical hypothyroidism.
- The sample was not restricted to hospital centers and was racially and geographically diverse
reflecting real life estimates in the US regarding thyroid hormone replacement
in pregnant women with subclinical hypothyroidism.
- The main
limitations of this study would be its
retrospective observational design and use of administrative claims
information, with a possible lack of clinical detail, improper classification
of treatment and confounders, and selection biases related to health plan
enrolment, treatment choice and diagnostic testing.
- Based on the study findings, it is
recommended that physicians follow a
policy of shared decision making approach with the patient to enable them
to participate in decision making about their health and treatment that would
be optimal for them.
- The timing of thyroid hormone replacement also becomes important.
preventing fetal loss is the main aim of thyroid replacement, treatment could
be restricted to the first trimester when the risk of fetal loss is the
- If treatment is initiated, regular monitoring of
thyroid function and dose adjustment is critical.
research is necessary to understand the causal association between fetal loss
and hypothyroidism and to evaluate the safety of thyroid hormone replacement in
results of such future studies would go a long way in helping both the
physician and the patient make informed decisions regarding starting thyroid
hormone replacement in pregnant women.
- Spyridoula Maraka, Raphael Mwangi, Rozalina
G McCoy, Xiaoxi Yao, Lindsey R Sangaralingham, Naykky M Singh Ospina, Derek T
O'Keeffe, Ana E Espinosa De Ycaza, Rene Rodriguez-Gutierrez, Charles C
Coddington III, Marius N Stan, Juan P Brito, Victor M Montori. Thyroid hormone
treatment among pregnant women with subclinical hypothyroidism: US national
assessment. The British Medical Journal (2017)
- High prevalence of subclinical hypothyroidism
during first trimester of pregnancy in North India - (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3683205/)