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Maternal Smoking Compromises Foetal IGF-1 Concentrations and Reduces Birth Weight: Presented at ENDO

By Paula Moyer

Special to DG News

SAN FRANCISCO, CA -- June 24, 2002 -- Maternal cigarette smoking is linked to reduced insulin-like growth factor-1 (IGF-1) concentrations in umbilical cord blood.

According to investigators who presented these findings at ENDO 2002, the 84^th annual meeting of the Endocrine Society, these findings may further elucidate the mechanism by which maternal smoking is inversely related to birth size.

The study also showed that infants born to smokers who quit during early pregnancy had higher birth weights and cord IGF-1 concentrations than those who continued to smoke, said lead investigator Peter C. Hindmarsh, MD, a paediatric endocrinologist at the University College in London, United Kingdom.

The investigators analysed cord IGF-1 concentrations, birth and placental size by maternal smoking status in the babies of Caucasian mothers. All the women's pregnancies were singleton; the investigators confined the analysis to pregnancies that were carried to term. They excluded pregnancies complicated by factors known to be associated with chronic hypoxia, including antepartum haemorrhage, pregnancy-induced hypertension and preeclampsia, as well as compromised uterine blood flow. Of the initial database of 1,650 mothers, the final number included in the analysis was 1,092.

Dr. Hindmarsh and colleagues assessed foetal prenatal growth and uterine blood flow at 20 and 32 weeks gestation. Mean birth weight, which was expressed as a standard deviation score (SDS), was +0.09 (SD 0.97). Placental weight averaged 676 g (SD 130). The mean cord IGF-1 concentration was 68.8 ng/ml (SD 25.4).

There was a clear effect of number of cigarettes smoked during pregnancy on cord IGF-1 and birth size, the investigators reported. For non-smokers, the mean birth weight SDS was 0.18; for infants whose mothers stopped early in pregnancy, it was 0.04. The mean SDS was -0.28 if the mother smoked less than 10 cigarettes/day, -0.20 with 10-20 cigarettes/day, and -0.24 for more than 20 cigarettes/day (p<0.001).

Cord IGF-1 concentrations averaged 70.2 ng/ml for infants born to non-smokers. For those who stopped early in pregnancy, the mean cord IGF-1 concentration was 70.4 ng/ml. In mothers who smoked less than 10 cigarettes/day, the mean concentration was 64.3 ng/ml. Concentrations averaged 60.7 ng/ml when mothers smoked 10-20 cigarettes/day, and 64.9 ng/ml when mothers smoked more than 20 cigarettes/day (p<0.01).

The mean placental weight did not vary significantly: 677 g for non-smokers, 673 g for those who stopped early in pregnancy, 670 g with less than 10 cigarettes/day, 671 g 10-20 cigarettes/day, and 672 g for more than 20 cigarettes/day.

The investigators noted that neither cord IGF-2 concentrations nor cord pH were influenced by the numbers of cigarettes smoked. However, cord IGFBP3 concentrations paralleled those of IGF-1, and cord GH concentrations increased with the daily cigarette dose (p<0.001). Although placental Grannum grading was strongly related to cigarette smoking (p<0.001), the smoking effect on IGF-1 and birth weight was maintained when the analysis took this factor into account.

"With the findings regarding IGF-1 concentrations, we have a clearer understanding of the effect of maternal cigarette smoking on infant birth size, and on foetal brain growth," Dr. Hindmarsh said. "If a woman stops smoking during the first trimester of pregnancy, she reduces the risk of ischaemic damage to the placenta, and the foetal outcomes are similar to those of a nonsmoker."

Because it is still unclear which component of cigarette smoking compromises the foetus, it is unclear whether smoking cessation aids such as nicotine replacements would be safer in pregnancy than smoking, he said.

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