You already know that maternal smoking during pregnancy is a big no-no, carrying numerous serious health risks for the unborn baby including fetal mortality, low birth weight, premature birth as well as a range of serious birth defects such as cleft palate, club foot and heart problems.

But for moms-to-be, even passive smoking raises the risks of stillbirth or having babies with birth defects, an analysis of 19 studies has found.

According to the report published in Pediatrics, stillbirth was 23 percent more common and birth defects were 13 percent more common among women who were exposed to secondhand smoke at home by their partners or in the workplace by colleagues.

Although the research did not find an increased risk of miscarriage or newborn death from secondhand smoke, and no specific birth defect was associated with secondhand smoke, the overall increased risk was seen after the results from all the studies were pooled.

The message is clear: It is imperative that women be protected from passive smoke exposure both pre-conception and throughout pregnancy, the researchers stress.

Fathers, too, play an vital role. Because they're often the primary source of secondhand smoke, dads who smoke should be more aware of the danger they pose to their unborn child.

It is still unclear whether the increased risk was due to the mother inhaling the father's secondhand smoke or if his smoking was affecting his sperm, explains Dr Jo Leonardi-Bee, of the UK Centre for Tobacco Control Studies at the University of Nottingham in England and one of the authors of the study.

But one thing is for sure: Smoking has already been proven to have an impact on sperm development, so it is very important that men quit smoking before trying for a baby, adds Dr Leonardi-Bee.