The safety of marijuana consumption by pregnant women is a controversial topic. While some doctors suggest that cannabis can be helpful to help control nausea, others offer dire warnings about potential developmental consequences for the fetus.

A recent study published in the Journal of Perinatology makes an effort to cut through some of the confusion. The researchers concluded that marijuana use by pregnant women did not create any increased risk for negative outcomes for the mother or for fetal abnormalities. Cannabis consumption was, on the other hand, associated with an increased risk of fetuses that were small for their gestational age, and for babies that were admitted to neonatal intensive care.

The study looked at 6,468 women, including 361 who used marijuana while pregnant. Among the outcomes for mother and fetuses that researchers evaluated were preterm delivery, pre-eclampsia, gestational diabetes, C-section, fetal growth restriction, stillbirth, and mortality.

This research adds to a growing, if inconclusive, library on the health effects of cannabis on pregnancy. There have never been clinical studies where pregnant women were specifically provided with marijuana and compared to control groups, so consequently, studies conducted on marijuana use and birth outcomes rely on honest self-reporting from the mothers. The data can often be clouded because women might also ingest alcohol, tobacco and other substances, making it impossible to know for sure what input caused a specific effect. Furthermore, the retrospective nature of the studies makes it difficult to control for nutrition and other environmental factors.

That’s why, although there are studies that suggest that children who were exposed to marijuana in utero could face long-term cognitive, behavioral or mental health consequences, even the National Institute on Drug Abuse acknowledges that more research is needed to verify whether negative outcomes are actually provoked by cannabis, or if other factors are at play. Notably, poverty is frequently a factor, which comes with its own overlapping and cascading risk factors.

Importantly, the Journal of Perinatology study — which adjusted for maternal age, race, parity, body mass index, and access to prenatal care — excluded women who used multiple substances and separated out results for women who used tobacco, providing results with more credibility than some of the other studies.

Elsewhere in the world, the use of cannabis to help induce and sooth the childbirth process can be dated back to at least the 7th century in Chinese and Persian traditions, and it has been used in other cultures as well to manage pain and nausea related to pregnancy. A study conducted in the 1990s in Jamaica, where cannabis does not have the same stigma as in the United States, found that children whose mothers smoked while pregnant actually developed faster in the 30 days after birth, although the study acknowledges that those children also tended to come from higher socio-economic levels than those from the non-smoking group.

For now, what researchers don’t know about the effects of marijuana on fetal health and development far outweighs what they do know, and good quality research is difficult to perform due to legal and ethical barriers facing scientists.

“Unfortunately, there is not a definitive answer to this question available at this time,” Paul Armentano, deputy director of NORML, notes in a review of the scientific literature. “Let’s hope that it is science — not rhetoric — that ultimately is the final arbiter in this decades-long debate.”