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Low Maternal Caffeine Intake Linked to Fetal Growth Restriction

Even small amounts of caffeine consumed during pregnancy may increase the risk for fetal growth restriction, according to a BMJ study.

Using questionnaires and saliva samples, researchers assessed the caffeine consumption of 2600 healthy pregnant women throughout pregnancy.

After adjustment for tobacco and alcohol use, women who consumed over 200 mg of caffeine daily (roughly 2 cups of brewed coffee) were at increased risk for fetal growth restriction (birth weight less than the 10th percentile), compared with women who consumed less than 100 mg. This finding was consistent for consumption across all trimesters. Women who reduced their caffeine intake had infants with a higher mean birth weight, relative to those who maintained their prepregnancy intake.

The authors suggest that women who are contemplating pregnancy should consume fewer caffeinated foods and beverages. "Once pregnancy is confirmed, they should make every effort to stop or markedly reduce caffeine consumption."

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Maternal caffeine intake during pregnancy and risk of fetal growth restriction: a large prospective observational study
- BMJ 2008;337:a2332

Objective
To examine the association of maternal caffeine intake with fetal growth restriction.

Design
Prospective longitudinal observational study.

Setting
Two large UK hospital maternity units.

Participants
2635 low risk pregnant women recruited between 8-12 weeks of pregnancy.

Investigations
Quantification of total caffeine intake from 4 weeks before conception and throughout pregnancy was undertaken with a validated caffeine assessment tool. Caffeine half life (proxy for clearance) was determined by measuring caffeine in saliva after a caffeine challenge. Smoking and alcohol were assessed by self reported status and by measuring salivary cotinine concentrations.

Main outcome measures
Fetal growth restriction, as defined by customised birth weight centile, adjusted for alcohol intake and salivary cotinine concentrations.

Results
Caffeine consumption throughout pregnancy was associated with an increased risk of fetal growth restriction (odds ratios 1.2 (95% CI 0.9 to 1.6) for 100-199 mg/day, 1.5 (1.1 to 2.1) for 200-299 mg/day, and 1.4 (1.0 to 2.0) for >300 mg/day compared with <100 mg/day; test for trend P<0.001). Mean caffeine consumption decreased in the first trimester and increased in the third. The association between caffeine and fetal growth restriction was stronger in women with a faster compared to a slower caffeine clearance (test for interaction, P=0.06).

Conclusions
Caffeine consumption during pregnancy was associated with an increased risk of fetal growth restriction and this association continued throughout pregnancy. Sensible advice would be to reduce caffeine intake before conception and throughout pregnancy.