Flu shots are a must have during pregnancy to make sure mother and baby do not get severely ill. For years, the Centers for Disease Control and the World Health Organization have recommended that pregnant women get seasonal flu vaccines. But now scientists have found evidence that flu vaccinations actually improve the quality of pregnancy, and may possibly increase the odds for a successful IVF (in vitro fertilization) cycle. If you are trying to get pregnant, then you definitely want to listen up.

A recent article in Science Magazine highlighted two clinical trials that are currently being done by the Center for Human Reproduction to determine whether giving women flu shots before they begin an IVF cycle can improve success rates. The scientists conducting these studies think that the vaccinations can increase the chances of implantation by stimulating a woman’s immune system to accept the embryo. They expect to see better implantation rates and fewer miscarriages from the flu shot.

They think this is possible because of the relationship between the immune system and reproduction. Women must have a strong and active immune system for a healthy pregnancy to occur. An increase in molecules that promote inflammation helps ensure that the lining of the uterus is ready to receive an embryo – a process called immunological tolerance. The flu shots are expected to stimulate molecular pathways that keep tolerance from breaking down too early. The scientists wonder if the flu vaccine can have this effect late in pregnancy, then maybe it can also help early in pregnancy as well.

In one of the trials, women will receive a flu shot or a placebo injection 10 days before they begin an IVF cycle. The researchers will assess whether the women who got the actual vaccines were more likely to become pregnant. They will also look at the levels of immune molecules in their blood to determine if tolerance occurred. The second trial will follow the same protocol except that the women will use embryos created from donor eggs instead of their own eggs. The research team intends to work with other fertility clinics to study about 1500 women in all.

One thing to keep in mind, however, is that the impact on fertility is still expected to be limited because researchers estimate that only about 15 percent of miscarriages happen because of a lack of tolerance. Instead, most occur because the embryo has chromosome abnormalities which the flu vaccine will not have an impact on.

The scientists working on these current trials came up with their hypothesis based on a few recent studies showing how flu shots have improved pregnancy. A 2014 study intended only to confirm the safety of flu vaccines during pregnancy ended up finding that it actually protected the baby by reducing the occurrence of stillbirths.  

Next, a 2016 study published in Clinical Infectious Diseases reported that stillbirths were half as common in women who received a flu shot during pregnancy than those who did not receive the shot. Researchers in Western Australia analyzed data from 60,000 births during the 2012 and 2013 seasonal influenza epidemics. They found that women who received the vaccine during pregnancy were 51 percent less likely to experience a stillbirth than the unvaccinated expectant mothers

Finally, another study from 2016 determined that women in Laos who had gotten a flu shot were 41 percent less likely to give birth prematurely. They had a reduced risk of delivering a preterm infant during the flu season. The research found that overall, vaccination may prevent one in five preterm births.