Oh baby, baby, how are you supposed to know whether Covid-19 vaccines can affect your placenta? Well, one thing you can do is pay attention to scientific studies like the one just published as a research letter in the medical journal Obstetrics & Gynecology that actually looked at placentas rather than posts on social media that merely speculate about placentas.

Why are people looking at and speculating about placentas? After all, the placenta may not be something that comes up in every day conversations as in “good to meet you, what do you think about placentas” or “you’re on mute, try looking at the placenta,” while on Zoom. Nevertheless, the placenta is essential for a successful pregnancy and birth. It’s an organ that emerges during pregnancy and connects the wall of your uterus to your fetus via an umbilical cord, connecting your blood supply with your fetus’s.

Think of the placenta as a combination Doordash, oxygen delivery service, and toilet bowl for your fetus, providing nutrients and oxygen while removing waste products. Studies have shown that severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections in the mother can lead to changes in the placenta such as decidual arteriopathy, fetal vascular malperfusion, and chronic histiocytic intervillositis. These may not be words that every day people use every day. However, if you happen to be a placenta with ears, you don’t want to hear words like these because such changes have been linked to worse birth outcomes.

According to the Centers for Disease Control and Prevention (CDC), those pregnant are at greater risk for more severe Covid-19 than those not pregnant when infected with the SARS-CoV2. SARS-CoV2 infections could increase the risk of worse birth outcomes too, such as pre-term birth. Getting the Covid-19 vaccine is not the same as being infected with the virus because the vaccine does not contain the live virus. The vaccine only gives your cells the “blueprints” to make just the spike proteins that stud the surface of the SARS-CoV2. This in turn exposes your immune system to the spike protein and essentially says, “get ready for anything that happens to have these spike proteins.” These are the spike proteins that making the virus look somewhat like a spiky massage ball or the ball at the end of one of those maces used in BDSM, not that you would know anything about that. The spike protein alone cannot give you Covid-19, just like Jennifer Aniston’s hair alone cannot act in an episode of the television show Friends. Nevertheless, it does make sense to look at what may happen to the placenta in those who have received the Covid-19 vaccine.

Note that look at the placenta doesn’t mean make claims about what Covid-19 vaccines may do to the placenta and fertility without providing real scientific evidence. As Nina Shapiro, MD, covered for Forbes on December 27 last year, soon after the Pfizer/BioNTech and Moderna Covid-19 mRNA vaccines began rolling out, claims on social media began rolling out that these vaccines could cause infertility. People or bots or both have been asserting that syncitin-1, a protein that helps keep the placenta attached to the uterus during pregnancy, is very similar to the SARS-CoV2 spike proteins. The claim was that the Covid-19 vaccines designed to stimulate an immune response against the spike protein would in turn also stimulate an immune response against syncitin-1.

Ah, but there is one itty bitty big problem with that theory. Syncitin-1 is not similar to the spike protein. Comparing the two would be a bit like comparing Brad Pitt with an arm pit. Sure there may be a few similarities between the two, like a few amino acids. But as a whole they are quite different. An immune response against the spike protein won’t necessarily affect syncitin-1, and having dinner with Pitt may not be the same as having dinner with an arm pit, unless, of course, it is Pitt’s pit.

With all of this as a backdrop, a team from the Feinberg School of Medicine at Northwestern University (Elisheva D. Shanes, MD, Sebastian Otero, Leena B. Mithal, MD, MSCI, Chiedza A. Mupanomunda, Emily S. Miller, MD, MPH, and Jeffery A. Goldstein, MD, PhD) then conducted the study described by the research letter in Obstetrics & Gynecology. They checked the placentas from 84 women who had received Covid-19 vaccines during pregnancy and 116 women who had not been vaccinated but had not tested positive for the SARS-CoV-2.

It turned out that the women who had been vaccinated were not more likely to have decidual arteriopathy (10% versus 12%), fetal vascular malperfusion (6% vs. 7%), low-grade chronic villitis (12% vs. 8%), or chronic histiocytic intervillositis (0% vs. 1.7%) than the women who hadn’t received the Covid-19 vaccine. In fact, high-grade chronic villitis occurred more often (14%) in those who had not been vaccinated (5%). There was also no real difference in how long the pregnancy went before the mother delivered the baby (an average of 38.5 weeks vs. 38.4 weeks), although those vaccinated were more likely to have had a vagina delivery (79% vs. 65%).

Granted this was not a super-large study. But findings from the study do add to the growing body of evidence that Covid-19 vaccines don’t bring any additional safety concerns for those who are pregnant or want to become pregnant. For example, last month the New England Journal of Medicine published some preliminary findings on 3,958 people who had identified themselves as pregnant and had received Covid-19 vaccines. At the time, 827 had already completed their pregnancies. The percentage that had yielded live births (86.1%) and the percentages of preterm births (9.4%) and other adverse outcomes weren’t really that different from reported percentages for the general population before the Covid-19 pandemic. I covered for Forbes back in February some of the other evidence.

All of this evidence is why the CDC website says, “if you are pregnant, you can receive a Covid-19 vaccine. Getting a Covid-19 vaccine during pregnancy can protect you from severe illness from Covid-19,” and “if you are trying to become pregnant now or want to get pregnant in the future, you can receive a Covid-19 vaccine.” The CDC does add that “there is currently no evidence that any vaccines, including Covid-19 vaccines, cause fertility problems—problems trying to get pregnant.” Of course, studies of Covid-19 vaccines, fertility, and pregnancy should continue. That doesn’t mean that the Covid-19 vaccines are considered “experimental” though. “Being studied” doesn’t mean “experimental.” Otherwise, nearly everything around you and that goes on or in you every day could be considered “experimental.”