Smoking Before and After Conception is Associated With Delayed Embryonic Development

It is common knowledge that smoking isharmful. In particular, it poses a significant risk to mother and child during pregnancy. According to research, nicotine consumption by mothers in the period immediately before and after conception is associated with delayed embryonic development, smaller fetuses at the time of the 20-week ultrasound examination, and lower birth weight.

Smoking Has a Harmful Effect on the Embryo

The study, published in Human Reproduction, one of the world’s leading journals in reproductive medicine, followed 689 women with singleton pregnancies between 2010 and 2018. The researchers found that in women who smoked ten or more cigarettes a day, , compared to non-smokers, embryonic development was delayed by almost a day by the tenth week of pregnancy, and by 1.6 days for smokers who had conceived through in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI). They also found that embryos could not “catch up” in their development over the course of the pregnancy, and were more likely to be born small for gestational age and had a 93-gram lower average birth weight than babies whose mothers were non-smokers.

This is the first study to examine the association between maternal smoking from 14 weeks before conception to 10 weeks after conception (the periconceptional period) and embryo development, looking at the external and internal shape of the embryo (morphology) during ongoing pregnancy. The researchers used virtual reality to study the development of the embryos and compared the morphology with the established stages of embryonic development, known as the Carnegie stages. Dr. Melek Rousian, gynecologist at Erasmus MC, University Medical Center, Rotterdam, the Netherlands, who led the study, said: “One of the most important findings of this study is that embryonic delay due to maternal smoking in the periconception phase is also associated with smaller fetal measurements at 20 weeks’ ultrasound and lower birth weight. Part of the fetal and neonatal outcomes can be explained by smoking during periconception and embryonic delay.”

The Carnegie stages only cover embryonic development for the first 10 weeks of gestation, so the researchers could not compare the embryo forms to an agreed standard beyond this stage. Instead, the ultrasound scans and birth weights provided developmental information, including head circumference, abdominal circumference and thigh bone length. “The effects of maternal smoking in periconception on embryonic developmental delay appear to be greater in the second trimester of pregnancy than at birth,” Dr. Rousian said. “We assume that there may be some catch-up growth in the second and third trimesters, but the delay in morphological development cannot be fully compensated for during the course of the pregnancy, as the ultrasound examinations after 20 weeks and the birth weights show.”

The mothers were part of the ongoing Rotterdam Periconceptional Cohort, a large prospective study embedded in the patient care of the Department of Obstetrics and Gynecology at Erasmus MC, University Medical Center, Rotterdam, a hospital providing maximum care for preconception and prenatal care. Consequently, they do not represent the general population. However, Dr. Rousian said the findings are important for all women planning a pregnancy. The findings of this study underscore the importance of quitting smoking before conception and that efforts to support women to stop smoking should focus on this window of opportunity, according to the researchers. If possible, women should quit smoking from the moment they plan to become pregnant, but it is always important to quit, especially at any stage of pregnancy. Smoking not only affects the growth of the embryo during pregnancy and birth weight, but also the development of the embryo in the earliest stages of pregnancy.

Effective Smoking Cessation Important

“We demonstrated a dose-response effect of maternal smoking on fetal morphology and growth; the more cigarettes a woman smoked, the greater the developmental delay. This underscores the importance of public health initiatives to promote preconception education and care, including effective smoking cessation programs for couples.” Dr. Rousian and her colleagues are studying how best to help expectant parents stop smoking, using one-on-one counseling sessions, follow-up visits, and digital lifestyle interventions. They believe this is important because numerous studies have shown that factors influencing the development of the fetus can affect health not only during pregnancy but also later in life.

“That is why the period before conception is an important area of research, as many future parents are unaware that an embryo is developing in the first few days when a pregnancy has not yet been confirmed,” said Dr. Rousian. New developments such as better imaging techniques, including virtual reality, have made it possible to study embryo development in much more detail, rather than relying on information from laboratory research. The study’s first author, Dr. Carsten Pietersma, PhD student and ultrasound diagnostician at Erasmus MC, said: “Since smoking is known to negatively affect fetal growth during pregnancy, we wanted to investigate how this may also affect embryo development. This developmental morphological study using Carnegie stages takes into account multiple dimensions of the embryo, rather than just one growth parameter.”