To investigate these issues the Danish National Birth Cohort (Better health for mother and child) was established. A large cohort of pregnant women with long-term follow-up of the offspring was the obvious choice because many of the exposures of interest cannot be reconstructed with sufficient validity back in time. The study needs to be large, and it is aimed to recruit 100,000 women early in pregnancy, and to continue follow-up for decades. The Nordic countries are better suited for this kind of research than most other countries because of their population-based registers on diseases, demography and social conditions, linkable at the individual level by means of the unique ID-number given to all citizens. Exposure information is mainly collected by computer-assisted telephone interviews with the women twice during pregnancy and when their children are six and 18 months old. Participants are also asked to fill in a self-administered food frequency questionnaire in mid-pregnancy. Furthermore, a biological bank has been set up with blood taken from the mother twice during pregnancy and blood from the umbilical cord taken shortly after birth. Data collection started in 1996 and the project covered all regions in Denmark in 1999. By August 2000. a total of 60,000 pregnant women had been recruited to the study. It is expected that a large number of gene-environmental hypotheses need to be based on case-control analyses within a cohort like this.

Surveillance of drug safety in pregnancy often draws on administrative prescription registries. Noncompliance in the use of prescribed medication may be frequent among pregnant women owing to their fear of fetotoxic side effects. To estimate compliance in the use of prescription drugs dispensed during pregnancy, we compared prescription data from the North Jutland Prescription Database with information on drug use provided by pregnant women to the Danish National Birth Cohort (DNBC), which is a health interview survey. We used the North Jutland Prescription Database to identify all prescription drugs dispensed during pregnancy for the 2,041 women who were enrolled in the DNBC in the County of North Jutland, Denmark. Compliance was defined as the probability of reporting drug use in DNBC after purchasing a dispensed prescription drug. The overall compliance to drugs purchased within 120 days before the interview was 43% (95% confidence interval = 40-46). Drugs used for treating chronic diseases, for example, beta-blockers, insulin, thyroid hormones, and diuretic and antiepileptic drugs, were always reported to be used, but compliance was low for drugs used for local or short-term treatment such as antihistamines, antibiotics, antacids, nonsteroid anti-inflammatory drugs, and gynecologic drugs. Thus, for the latter drug groups the prescription database may provide an incomplete identification of exposure. Neither data source is unbiased regarding actual drug intake. Nevertheless, our results indicate that for some drug groups risk assessment studies based on prescription data may produce false negative results as a result of noncompliance.

The results indicate that maternal smoking during pregnancy may increase the risk of IC.

WHAT'S KNOWN ON THIS SUBJECT: Infantile colic affects almost 10% of all infants and is characterized by crying and fussing in an otherwise healthy and well-fed infant. Prenatal exposure to tobacco smoking is a risk factor, but it is unclear whether nicotine causes the association.WHAT THIS STUDY ADDS: Infants exposed to nicotine replacement therapy during pregnancy had elevated infantile colic risk of the same magnitude as infants exposed to tobacco smoking. Intrauterine exposure to nicotine may play a causal role in the pathogenesis of infantile colic. abstract OBJECTIVE: To investigate the associations between use of nicotine replacement therapy (NRT) and smoking during pregnancy and infantile colic in the offspring. METHODS:We used data from maternal interviews (from pregnancy and at 6 months post partum) from the Danish National Birth Cohort (1996)(1997)(1998)(1999)(2000)(2001)(2002). We included 63 128 live-born singletons with complete information on nicotine exposure during pregnancy and infantile colic symptoms as recorded at 6 months of age. RESULTS:A total of 46 660 infants (73.9%) were unexposed to nicotine during pregnancy; 207 (0.3%) were exposed to NRT, 15 016 (23.8%) were exposed to smoking, and 1245 (2.0%) to both. A total of 4974 (7.9%) infants fulfilled Wessel' s modified criteria for infantile colic. Prenatal nicotine exposure was associated with elevated risk for infantile colic in the offspring. Compared with the unexposed, NRT users had an adjusted odds ratio (OR) (95% confidence interval) of 1.6 (1.0-2.5; P = .03), smokers had OR = 1.3 (1.2-1.4), and women who both smoked and used NRT had OR = 1.6 (1.3-1.9). Partners' smoking was not associated with infantile colic after adjustment for maternal smoking. CONCLUSIONS:We corroborated the association between smoking and infantile colic after adjustment for several possible confounders in a large cohort study. Moreover, we found that infants exposed to NRT prenatally had an increased risk for infantile colic of the same magnitude as those exposed to tobacco smoke. Thus, nicotine may play a role in the pathogenesis of infantile colic. Pediatrics 2012;129:e652-e658 AUTHORS:

We observed an increased risk of infantile colic in preterm and small for gestational age infants in a large cohort. Our results suggest that the aetiology of infantile colic may be found in the prenatal, perinatal, and neonatal period.