Grand Rounds

Is Preconception Thyroid Function Associated with Adverse Birth Weight Outcomes?

BACKGROUND AND PURPOSE:

Du et al. (The Journal of Clinical Endocrinology & Metabolism, 2022) focus on the impact of preconception maternal TSH and pregnancy outcomes

Population-based cohort study
- National Free Preconception Checkups Project in China
Population
- Pregnancies between 2010 to 2012
Exposures
- Maternal TSH level in 6 months before pregnancy
Study design
- Regression models used to
  - Examine dose-response relationships
  - Estimate potential optimal cutoff values
- Logistic regression was used to assess the relationship between different TSH groups and the risk of adverse outcomes
Primary outcome
- Pregnancy outcomes (e.g., stillbirth, preterm birth)
- Birth weight outcomes (e.g., small for gestational age [SGA], large for gestational age [LGA], low birth weight [LBW})

175,112 women
Lower preconception TSH was associated with a higher odds of
- LBW (P=0.003)
- Preterm delivery (P<0.001)
There was no significant association between preconception TSH and
- SGA
- Macrosomia
- Fetal anomalies
- Stillbirth
- Natural or induced abortion
- Cesarean delivery
Compared with TSH levels between 0.91 to 1.82 mIU/L, low and high levels of TSH were associated with a higher risk of preterm delivery and LGA
- Low levels: < 0.40 mIU/L | 0.40 to 0.90 mIU/L
- High levels: 1.83 to 2.49 mIU/L | 2.50 to 3.99 mIU/L | >4.00 mIU/L
There was no significant association between TSH groups and the risk for LBW, except for TSH < 0.40 mIU/L

Preconception TSH levels were associated with increased risks LGA, LBW, and preterm delivery
Both high and low levels of preconception TSH (J-curve) were associated with an increased risk of preterm delivery and large for gestational age
Preconception TSH levels between 0.91 to 1.82 mIU/L appears to be an optimal range for avoiding adverse pregnancy outcomes

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