Does Late Implantation Cause Miscarriage?

The timing of when a fertilized egg implants in the uterus affects the chances of whether it can develop successfully. Implanting too early or too late may mean the uterine lining and the body's hormone levels do not provide optimal support for the embryo. While late implantation can be a factor in miscarriage, it is not something anyone can control or prevent.

Timing of Ovulation and Implantation

When you ovulate, halfway through your menstrual cycle, an egg is released from your ovary into one of your fallopian tubes. On average, the egg has 24 hours to be fertilized before it is no longer viable.

During conception, the egg is fertilized in the fallopian tube and then travels along the tube to make its way into the uterus. Once in the uterus, the egg implants itself into the lining (endometrium) of the uterus. The implantation process takes about 48 hours.

The spot where the embryo attaches itself inside of the endometrium can disrupt some blood vessels, which may cause some light bleeding anywhere from five to 10 days after conception, but before your period would typically occur. However, not everyone bleeds. Lack of bleeding doesn't mean you aren't pregnant or that you don't have late implantation.

Late Implantation and the Risk of Miscarriage

Several studies have found a higher risk of miscarriage in pregnancies where implantation occurs more than eight to 10 days after ovulation. A classic study published in the New England Journal of Medicine found that the likelihood of miscarriage increased significantly with every day of late implantation after day nine.

On the ninth day, the likelihood of miscarriage was 13%. On day 10, it was 26%, and on day 11 the rate was 52%. Any later than 11 days and the risk of miscarriage increased to 82%. What exactly these findings mean, however, is debatable.

Late implantation, by itself, is unlikely to be a direct cause of miscarriage. Embryos with chromosomal abnormalities are more likely to miscarry. If an embryo has a chromosomal anomaly, the abnormal genetic material may also cause the embryo to implant later than usual.

Another theory is that some factor in the uterine lining could cause problems during implantation and that this could lead to miscarriage. However, researchers are still studying the matter.

Causes of Late Implantation

A study of late implantation found that current smoking was a risk factor for late implantation. If you are trying to become pregnant, this is one of many reasons to quit smoking.

But other than that, the timing of implantation isn't under anyone's control. Beyond having an in vitro fertilization procedure in which a fertilized egg is transferred directly into the uterus, there is no way to speed up an egg's trip down the fallopian tubes to the uterus. And once the egg is in the uterus (whether through IVF or not), there is no way to force it to embed in the uterine lining.

A Word From Verywell

There is no evidence that late implantation by itself causes miscarriage. However, the later the egg implants, the more likely miscarriage is to occur. If you have menstrual irregularities or if you have been struggling to conceive, talk to your doctor. Although there is no test to determine when embryos implant or why late implantation occurs, other tests may uncover the reasons behind impaired fertility.