Coffee and Pregnancy

The following study was published by the Institute for Scientific Information on Coffee (ISIC). We invite you to read this very interesting information.

Pregnancy

Overview

With the onset of nausea, vomiting and appetite loss in very early pregnancy occurs a drastic drop in coffee consumption and hence caffeine intake from coffee.
Women experiencing viable pregnancies are more likely to reduce their caffeine intake in response to the pregnancy signal than women who have a miscarriage.
Therefore, reduced caffeine consumption may be a consequence of pregnancy viability rather than increased consumption causing any reproductive complication.
The studies available from the last decade do not provide convincing evidence that moderate caffeine consumption (200-300 mg/day*) increases the risk of any reproductive or perinatal complication.
The evidence for an effect of caffeine on reproductive health and fetal development is limited by the inability to rule out plausible alternative explanations for some observed confounding associations, such as pregnancy symptoms, smoking and incorrect, or imprecise assessment of the duration of exposure.
Current recommendations for caffeine intake during pregnancy range from 200mg – 300mg per day from all sources i.e. not simply coffee.
* A regular cup of coffee contains approximately 100mg of caffeine.

Background information

It is widely accepted that any effects of coffee consumption on reproductive health are linked to caffeine rather than to coffee consumption per se. Hence the majority of the published work focuses on the effects of caffeine, not coffee, consumption.

In a recent review of the “Epidemiologic Evidence concerning the Reproductive Health Effects of Caffeine Consumption: A 2000-2009 Update”, J.D. Peck et al. scrutinized and reviewed scientific publications on the subject from the last ten years¹ and their findings are highlighted below. In addition, data from some of the more recent studies not reviewed by Peck et al.¹ are included.

Caffeine intake and fertility

Studies assessing the impact of caffeine on fertility have evaluated a variety of outcomes including time to pregnancy, infertility and semen quality.

Incorrect, or imprecise, assessments of the duration of exposure are a primary concern for the few recent studies addressing time to conception and ovulatory infertility. Potential recall bias and exposure misclassification may explain the modest association reported for coffee and tea consumption and increased time to pregnancy.

No support for an association with infertility due to ovulation disorders was provided, but exposure measurement error was likely introduced as a result of the timing of exposure assessments.

Evaluations of semen quality have consistently failed to observe adverse effects associated with caffeine intake¹, as confirmed by a recent Danish study².

In summary, consistent relationships between caffeine intake and measures of sub-fecundity have not been observed. According to a recent Australian review paper, at this point in time, the evidence from the literature is unclear and insufficient to provide coffee consumption guidelines for preconception advice³.

Caffeine intake and gestation

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 signal symptoms during the early weeks of pregnancy¹. For example, Lawson et al.⁴ reported that 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.

Thus, women experiencing viable pregnancies are more likely to reduce their caffeine intake in response to the pregnancy signal than women who will have a miscarriage. As a result, reduced caffeine consumption may be a consequence of pregnancy viability rather than increased consumption causing any reproductive complication (“reverse causation”).

Caffeine and miscarriage

The current evidence remains insufficient to draw conclusions regarding the potential role of caffeine in miscarriages.

A study by Wen et al.⁵ 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.⁶, based on which several professional associations have stated an upper safe limit for caffeine intake during pregnancy. The study is characterized 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.

More recently in 2010, a Chinese case-control study⁷ and a small US prospective cohort study⁸ 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 increases 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 association⁹.

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 miscarriage” ¹⁰.

Caffeine and pre-term labour

Large studies considering total caffeine intake have consistently reported no increased risk of delivery before 37 weeks of gestation¹.

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 birth”¹⁰.

Caffeine intake and fetal health

Caffeine and fetal growth

Studies of caffeine and fetal growth restriction are equivocal, with approximately half of the studies in a review¹ reporting weak associations with intrauterine growth restriction, or reduced birth weight, and half observing no effects.

In the Dutch Generation R Study – a prospective cohort study which included 7,346 pregnant women – consistent associations were observed between caffeine intake and fetal head circumference, or estimated fetal weight. Higher caffeine intake (over 540mg caffeine daily) was associated with shorter birth length, suggesting that fetal growth may be impaired by caffeine. However, further studies are needed to assess these associations in non-European populations and the possible postnatal consequences of the observed fetal growth restriction¹¹.

The 2010 Committee Opinion of the American College of Obstetricians and Gynecologists stated that the relationship between caffeine and growth restriction remains undetermined¹⁰.

Caffeine and congenital malformations

With a few exceptions, recent studies have not reported an increased risk of malformations with greater caffeine consumption¹. However, the body of evidence for any single malformation or subgroup is limited.

The modest association between total caffeine intake and anorectal astresia (birth defect in which the rectum is malformed)¹² could not confidently rule out potential sources of bias, such as selection bias due to missing data, exposure misclassification and confounding.

Two papers found no association between maternal caffeine intake during pregnancy and orofacial clefts (abnormal facial development during gestation characterised by cleft lip with or without cleft palate)^13,14.

One recent paper reported weak positive associations between maternal caffeine consumption and spina bifida (neural tube defects), but without a dose-effect relationship and with a negative association for tea. However, the control for confounding by smoking and alcohol (both yes/no answers only) was insufficient¹⁵.

The same research group raised the issue that gene variants like slow/fast caffeine metabolizers may run different risks¹⁶.

Caffeine and fetal death

As with studies of miscarriage, the interpretation of the work on caffeine and fetal death, which has consistently reported modest associations across studies, needs to consider that these studies may also share common sources of bias which may explain the observed relationship with caffeine use¹.

Recommendations for caffeine intake during pregnancy

Limiting caffeine during pregnancy – an intervention study

A review of the literature¹⁷ looked at the clinical basis for restricting the caffeine intake of mothers on fetal, neonatal and pregnancy outcomes. The authors selected only one Danish study meeting the criteria for a controlled study: women less than 20 weeks pregnant were randomly assigned to drinking caffeinated instant coffee (568 women) or decaffeinated instant coffee (629 women). The study found that reducing the caffeine intake of regular coffee drinkers during the second and third trimester by an average of 182mg/day (approximately 2 regular cups of coffee) did not affect birth weight or length of gestation. According to the study, there is insufficient evidence to confirm or refute the effectiveness of caffeine avoidance on birth weight or other pregnancy outcomes and high-quality, double-blind randomized controlled studies are needed to determine whether caffeine has any effect on pregnancy outcomes¹⁷.

Official recommendations for caffeine intake during pregnancy

A paper by Weng et al. published in 20086 created a degree of confusion surrounding the safe level of caffeine intake during pregnancy and led different organisations to provide different advice.

Following research¹⁸ carried out in the UK around the same time, the Food Standards Agency suggests an upper limit for pregnant women of 200mg of caffeine* per day from all sources, and this level is the same as that recommended by the March of Dimes in the USA.

However, also in the USA, the American Dietetic Association, in its 2008 Position Paper, suggests maintaining the previous commonly accepted limit of 300 mg per day as a safe upper limit and this is in line with the advice given by the EU Scientific Committee on Foodstuffs which states that “While intakes (of caffeine) up to 300 mg/day appear to be safe, the possible question of effects on pregnancy and the offspring at regular intakes above 300 mg/day remains open”.

* A regular cup of coffee contains approximately 100mg of caffeine.

Conclusion

The available scientific evidence does not support a positive relationship between caffeine consumption and adverse reproductive or perinatal outcomes. The studies available from the last decade do not provide convincing evidence that moderate caffeine consumption (200-300mg per day from all sources, not simply coffee) increases the risk of any reproductive complication.

On the whole, associations with subfecundity, preterm delivery and congenital malformations are not routinely observed. Studies of pregnancy loss and fetal growth have generated more interest due to the frequency with which adverse effects are reported in connection with caffeine use.

References
1.Peck J.D. et al. (2010), A review of the epidemiologic evidence concerning the reproductive health effects of caffeine consumption: a 2000-2009 update. Food Chem Toxicol, 48:2549-76.
2. Jensen T.K. et al. (2010), Caffeine intake and semen quality in a population of 2,554 young Danish men. Am J Epidemiol, 171:883-91.
3. Anderson K. et al. (2010), Lifestyle factors in people seeking infertility treatment – A review. Aust N Z J Obstet Gynaecol, 50:8-20.
4. Lawson C.C. et al. (2004), Changes in caffeine consumption as a signal of pregnancy. Reprod Toxicol, Jul;18(5):625-33.
5. Wen W. et al. (2001), The associations of maternal caffeine consumption and nausea with 6 spontaneous abortion. Epidemiology, 12:38-42.
6. Weng X et al. (2008), Maternal caffeine consumption during pregnancy and the risk of miscarriage: a prospective cohort study. Am J Obstet Gynecol, 198:279.e1-8.
7. Zhang B. et al. (2010), Risk factors for unexplained recurrent spontaneous abortion in a population from southern China. Int J Gynaecol Obstet, 108:135-8.
8. Pollack A.Z. et al. (2010), Caffeine consumption and miscarriage: a prospective cohort study. Fertil Steril, 93:304-6.
9. Greenwood D.C. et al. (2010), Caffeine intake during pregnancy, late miscarriage and stillbirth. Eur J Epidemiol, 25:275-80.
10. Committee on Obstetric Practice. (2010), Moderate caffeine consumption during pregnancy. Obstet Gynecol, 116:467-8.
11. Bakker R. et al. (2010), Maternal caffeine intake from coffee and tea, fetal growth, and the risks of adverse birth outcomes: the Generation R Study. Am J Clin Nutr, 91:1691-8.
12. Miller E.A. et al. (2008), Maternal exposure to tobacco smoke, alcohol and caffeine, and risk of anorectal atresia: National Birth Defects Prevention Study 1997–2003. Paediatr Perinat Epidemiol, 23:9-17.
13. Johansen A.M. et al. (2009), Maternal consumption of coffee and caffeine-containing beverages and oral clefts: a population-based case-control study in Norway. Am J Epidemiol, 169:1216-22.
14. Collier S.A. et al. (2009), Maternal caffeine intake during pregnancy and orofacial clefts. Birth Defects Res A Clin Mol Teratol, 85:842-9.
15. Schmidt R.J. et al. (2009), Maternal caffeine consumption and risk of neural tube defects. Birth Defects Res A Clin Mol Teratol, 85:879-89.
16. Schmidt R.J. et al. (2010), Caffeine, selected metabolic gene variants, and risk for neural tube defects. Birth Defects Res A Clin Mol Teratol, 88:560-9.
17. Jahanfar S. et al. (2009), Effects of restricted caffeine intake by mother on fetal, neonatal and pregnancy outcome. Cochrane Database Syst Rev, 15;(2):CD006965.
18. CARE Study Group. (2008), Maternal caffeine intake during pregnancy and risk of fetal growth restriction: a large prospective observational study. BMJ, 337.