Caffeine intake and gestation

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Caffeine intake in early pregnancy

A critical aspect of caffeine exposure includes the importance of measuring exposure to caffeine during the relevant time window and the need to capture changing intake patterns throughout pregnancy. Caffeine consumption tends to decrease during the early weeks of pregnancy, coinciding with increasing pregnancy symptoms and aversions1.

Pregnancy symptoms, including aversions to tastes and smells, nausea and vomiting are common in healthy pregnancies that result in live births, and occur less frequently among women whose pregnancies end in miscarriages. This relationship is attributed to a stronger pregnancy signal linked to higher concentrations of pregnancy hormones in viable pregnancies.

Caffeine consumption has been shown to decrease with increasing pregnancy symptoms during the early weeks of pregnancy1. For example, Lawson et al.6 reported that the mean onset of nausea, vomiting and appetite loss occurred between 5 and 6 weeks from the last menstrual period, accompanied by a 59% decrease in caffeine intake from coffee between weeks 4 and 6.

It may therefore be deduced that women experiencing healthy pregnancies are more likely to reduce their caffeine intake in response to pregnancy symptoms than women who will have a miscarriage. As a result, reduced caffeine consumption may be a consequence of pregnancy viability as opposed to increased consumption causing any reproductive complication (“reverse causation”).

One study describes patterns of dietary caffeine consumption before and after pregnancy recognition in a cohort of 8,347 American women who had recently given birth7. Maternal self-reported consumption of beverages (caffeinated coffee, tea, and soda) and chocolate the year before pregnancy was used to estimate caffeine intake. The proportions of pre-pregnancy caffeine consumption stratified by maternal characteristics are reported. Patterns of reported change in consumption before and after pregnancy were also examined by maternal and pregnancy characteristics. Adjusted prevalence ratios were estimated to assess factors most associated with change in consumption. About 97% of mothers reported caffeine consumption (average intake of 129.9 mg/day the year before pregnancy); soda was the primary source of caffeine. The proportion of mothers reporting dietary caffeine intake of more than 300 mg/day was significantly higher among those who smoked cigarettes or drank alcohol. Most mothers stopped or decreased their caffeinated beverage consumption during pregnancy. A high level of caffeine intake was associated with risk factors for adverse reproductive outcomes. The authors recommend further studies which may improve the maternal caffeine exposure assessment by acquiring additional information regarding the timing and amount of change in caffeine consumption after pregnancy recognition.

Data from the UK Caffeine and Reproductive Health (CARE) study were used to explore the relationship between maternal caffeine intake and nausea, vomiting and fetal growth restriction in pregnancy. No evidence of a relationship could be found. The strength of this study is the thorough assessment of caffeine exposure, however the extremely low response rate (20%) is a concern and a selection bias cannot be excluded8.

Coffee and Gestational Diabetes Mellitus

Gestational diabetes (or gestational diabetes mellitus, GDM) is a condition in which women without previously diagnosed diabetes exhibit high blood glucose levels during pregnancy (especially during their third trimester).

A population based cohort of 71,239 women taking part in the Danish National Birth Cohort examined the relation between first trimester coffee and tea consumption and gestational diabetes mellitus (GDM) risk. Coffee or tea intake was reported in 81.2% of the women (n = 57 882).  1.3% (n = 912) of pregnancies were complicated by GDM, and among non-consumers, 1.5% of pregnancies were complicated by GDM. After adjustment for age, socio-occupational status, parity, pre-pregnancy body mass index, smoking, and cola intake, there was suggestion of a protective, but non-significant association with increasing coffee (RR ≥8 versus 0 cups/day = 0.89 [95%CI 0.64-1.25]) and tea intakes (RR ≥8 versus 0 cups/day = 0.77 [95%CI 0.55-1.08]). Results were similar by smoking status, except a non-significant 1.45-fold increased risk with ≥8 coffee cups/day for non-smokers. There was a non-significant reduced GDM risk with increasing total caffeine. These results suggest that moderate first trimester coffee and tea intake is not associated with GDM increased risk, it may even have a protective effect9.

Caffeine and miscarriage

The epidemiological studies evaluating the risk of spontaneous abortion from caffeine exposure, as reviewed by Peck1 and Brent2 have been inconsistent. The most serious criticism is that the majority of these studies failed to evaluate the pregnancy signal.

A study by Wen et al.10 likely provides the best evidence for the pregnancy signal phenomenon to date. In this study, increased risk of miscarriage was only observed for caffeine consumed after nausea onset, but not for caffeine consumed before nausea onset, or among those without nausea.

Other persistent problems with the validity of studies of caffeine and miscarriage include confounding by smoking and potential recall bias. This is namely the case in a study by Weng et al.11 upon which several professional associations based an upper safe limit for caffeine intake during pregnancy. The study is characterised by incomplete control for confounding by the daily number of cigarettes smoked or the duration of nausea and vomiting (only yes/no answers). In addition, this study was only stratified for two levels of caffeine intake, lower or higher than 200mg daily and the latter group clearly includes very high levels of caffeine intake.

In 2010, a Chinese case-control study12 and a small US prospective cohort study13 did not find any association between caffeine consumption and the risk of miscarriage.

In contrast, a UK study reported that greater caffeine intake is associated with an increase in late miscarriage and stillbirth. However, they identified small numbers of late miscarriages and stillbirths, hence limiting the power to detect small associations and leading to considerable uncertainty in the size of the association14.

The 2010 Committee Opinion of the American College of Obstetricians and Gynecologists stated that “Moderate caffeine consumption (less than 200 mg per day) does not appear to be a major contributing factor in miscarriage; … a final conclusion cannot be made as to whether there is a correlation between high caffeine intake and miscarriage15.”

In a small retrospective case-control study conducted in Italy, it was concluded that caffeine might increase the risk of sine causa recurrent miscarriage. The authors indicate that a potential recall bias cannot be excluded due to the miscarriages and the controls being respectively interviewed late after their miscarriages and before the delivery. Furthermore, they suggest that women with altered reproductive history could tend to over-report their caffeine consumption and caution that further clinical studies are required before the information is used in clinical setting, to evaluate the relationship between lifestyle and recurrent miscarriage16.

Caffeine and pre-term labour

Large studies considering total caffeine intake have consistently reported no increased risk of delivery before 37 weeks of gestation1. This was confirmed by a meta-analysis, including 15 cohort studies and 7 case-control studies, where no important association between caffeine intake during pregnancy and the risk of preterm birth was observed17.

In addition, the 2010 Committee Opinion of the American College of Obstetricians and Gynecologists stated that “Moderate caffeine consumption (less than 200 mg per day) does not appear to be a major contributing factor in preterm birth15.”

A Polish study published in 2011 had the objective of estimating maternal caffeine intake during pregnancy and its influence on pregnancy duration, birthweight and the Apgar score of the newborn. It concluded that caffeine intake of no more than 300mg per day during pregnancy does not affect pregnancy duration and the condition of the newborn. Black tea was the major source of caffeine, whereas 26% of women gave up coffee during pregnancy. An underestimation of maternal caffeine intake during pregnancy could not be excluded, since the questionnaire was carried out on the last day before delivery18.

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