Study links maternal smoking to delayed embryonic development

A new study published in the reproductive medicine journal Human Reproduction has revealed that by the 10th week of pregnancy, embryo development was delayed by nearly a day in women who smoked 10 or more cigarettes a day compared to non-smokers.

MUMBAI: Smoking by mothers-to-be during the periconceptional period- from 14 weeks before conception up to 10 weeks after conception- can cause delayed embryonic development and lower birth weight, a new study published in the reproductive medicine journal Human Reproduction has revealed.

The researchers followed 689 women with singleton (birth of one child during a delivery) pregnancies between 2010 and 2018. (Representational Image/Shutterstock)

The researchers found that by the 10th week of pregnancy, embryo development was delayed by nearly a day in women who smoked 10 or more cigarettes a day compared to non-smokers and by 1.6 days in smokers who conceived by means of in vitro fertilisation (IVF) and intracytoplasmic sperm injection (ICSI).

The study also noted that embryos were not able to “catch up” with their development over the course of the pregnancy and were more likely to be born small for gestational age and with a median (average) birth weight 93 grams lower than babies born to non-smoking women.

“One of the key messages of this study is that the delay in embryonic development due to mothers smoking in the periconceptional period is also associated with smaller fetal measurements at the 20-week ultrasound scan and a lower birth weight,” lead author of the study, Dr Melek Rousian from University Medical Center, Rotterdam, The Netherlands was quoted in a media release.

The study followed 689 women with singleton (birth of one child during a delivery) pregnancies between 2010 and 2018. The researchers used virtual reality to look at the embryos’ development and compared the morphology against established stages of embryo development, commonly known as the Carnegie stages of human embryonic development.

“Smoking was assessed by asking every participant about smoking habits during the period 4 weeks prior to conception and during pregnancy. If the woman did smoke during this timeframe, the participant was asked how many cigarettes or other tobacco products she smoked, expressed as number per day. If the woman had quit smoking, the date of cessation was asked,” the study said.

Experts said the study has global consequences given the widespread prevalence of smoking. “In India, the consequences are graver because of smoking and smokeless form of tobacco used widely in urban as well as rural areas and across classes,” said Mumbai-based gynaecologist Dr Duru Shah. “Many studies have linked worse pregnancy outcomes to tobacco use. The metabolites or the end products of tobacco are linked to reduced quality of eggs and sperms. It is known to impact fertility and cause early menopause,” she said.

According to Shah, when women find out about their pregnancy, they immediately stop smoking, and any other unhealthy habits due to the concern for their babies. “The government should therefore plan the right kind of awareness campaigns that can highlight impacts of smoking and other tobacco use during the periconceptional period as well. Such campaigns can have long term impacts on tobacco use,” she said.

A 2021 study published in Population Medicine titled ‘Prevalence and predictors of tobacco use among currently married pregnant women in India’ showed that around 4.6% of pregnant women in the country use tobacco, and the smokeless form of tobacco use is predominant among pregnant tobacco users.

“The findings of the present study need to be used to reduce tobacco use among pregnant women in the country by identifying subpopulations at risk, and sensitising them to the harmful consequences of tobacco use, by offering tobacco cessation services during prenatal checkups,” the study said.

Delhi-based reproductive medicine specialist Dr Ashok Khurana, who is also the former president of the Society of Fetal Medicine said that passive smoke or second-hand smoke is also detrimental for pregnant women.

“It is a well-known fact that direct as well as passive smoking can lead to abnormal fetal growth as well as abnormal brain development. Many studies in the West have established these links,” he said adding that smoking among women in India is common across classes due to the wide variety and forms of tobacco available. In addition to cigarettes, smoking beedis and hookah is common in India. In smokeless forms, the use of roasted tobacco leaves, misri, gutkha, pan masala is common.