What about smoking marijuana during pregnancy.
It has been shown that administration of high doses of THC to animals lowers serum testosterone levels, impairs sperm production, motility, and viability, disrupts the ovulation cycle, and decreases output of gonadotropic hormones. According to the 1997 Merck Manual of Diagnosis and Therapy, fertility effects related to cannabis use are uncertain.
Research has demonstrated that human sperm contains receptors which are stimulated by substances like THC and other cannabis-related chemicals. Tests have implied that smoking of marijuana could impact the sperm's functions, though this impact is unknown. There is some evidence that cannabis may compromise female fertility with a modest association reported between cannabis use and infertility in Mueller et al.'s case controlled study of 150 women with primary anovulatory infertility. While Wenger et al. indicate evidence that THC and anandamide increase the duration of pregnancy and increase the frequency of stillbirth in rats.
In a report prepared for the Australian National Council on Drugs, Copeland, Gerber and Swift conclude that current understanding suggests cannabis-related substances are contraindicated in pregnancy, as are compounds that interact with endocannabinoid synthesis and metabolism
A 1989 study of 1226 mothers published in the New England Journal of Medicine concluded that "the use of marijuana or cocaine during pregnancy is associated with impaired fetal growth". Compared to fetal alcohol syndrome, similar types of facial features and related symptoms are not associated with prenatal marijuana exposure. THC passes into the breast milk and might affect a breastfed infant. Many studies about drug use during pregnancy are self-administered by the applicants and not always anonymous.
The stigma of using illicit drugs while pregnant or smoking marijuana during pregnancy discourages honest reporting and can invalidate the results. Studies show that women who consume cannabis while they are pregnant may also be likely to consume alcohol, tobacco, caffeine, or other illicit drugs, which makes it difficult to deduce scientific facts about just marijuana use from statistical results. Very few large, well-controlled epidemiological studies have taken place to understand the connection of marijuana use and pregnancy.
Some studies have found that children of tobacco and marijuana-smoking mothers more frequently suffer from permanent cognitive deficits, concentration disorders, hyperactivity, and impaired social interactions than non-exposed children of the same age and social background. A recent study, with participation of scientists from Europe and the United States, has now identified that naturally occurring endocannabinoid molecules play a role in establishing how certain nerve cells connect to each other in the fetal brain.
Another study examining cannabinoid receptor proteins (CBRs) expressed in brain cells of mice determined that endogenous endocannabinoids assist in directing brain cell directional development while in the womb. The researchers suggest that elevated blood THC levels due to cannabis consumption would affect brain development of human fetuses.
In contrast, other studies in Jamaica have suggested that smoking marijuana during pregnancy by expectant mothers does not appear to cause birth defects or developmental delays in their newborn children.
also see - Smoking during pregnancy.