When we talk about genetics, it's a mystery as to why we really exist. The further you study the world of DNA, the more questions you'll most likely end up having. Yet no matter how much you learn, there will never be a clear answer as to how we are who we are, or why sometimes things don't work out how they're supposed to. Molar pregnancies are one such example of things not working out.
Molar pregnancies occur in 1 out of every 1000 pregnancies. That's pretty rare- but then again, not so much when you remember how many people there are in the world. Also referred to as gestational trophoblastic disease (GTD) or hydatidiform mole, molar pregnancies occur when fertilization doesn't go quite as planned.
The Mayo Clinic states that there are two types of molar pregnancies: Complete and Partial/Incomplete. "In a complete molar pregnancy, an empty egg [(meaning mom's DNA is MIA)] is fertilized by one or two sperm", so all of the genetic material in the egg is only the father's. This obviously doesn't work to create new life. In this case, according to the American Pregnancy Association (APA), "the placenta grows and produces the pregnancy hormone, hCG," giving the appearance of a normal pregnancy. But once an ultrasound is done, you'll see that there's no fetus detected.
In a partial/incomplete molar pregnancy, the Mayo Clinic explains, "the mother's chromosomes remain [inside the egg] but the father provides two sets of chromosomes. As a result, the embryo has 69 chromosomes instead of 46". The APA elaborated that the embryo develops, but has severe birth defects and will be quickly consumed by abnormal cell growth.
The APA adds that the symptoms of a molar pregnancy include vaginal spotting/bleeding, nausea and vomiting, increased hCG levels, and high blood pressure (AKA early preeclampsia). The Mayo Clinic further lists that, "vaginal passage of grape-like cysts," and "pelvic pressure or pain," can also be symptoms. Once detected, a molar pregnancy either ends in miscarriage, or needs to be terminated. Even after the molar pregnancy ends one way or another, there could still be complications (which you can read more about here), so be sure that you and your doctor are on the same page about your condition.
There isn't a clear explanation as to why a molar pregnancy happens in the first place. But then again, there isn't a clear explanation as to why such mistakes happened in the first place. One thing is for sure though; if you experience a molar pregnancy, it isn't because you did something wrong. As with regular miscarriages, nature just so happened to miscalculate a few things during conception. Unfortunately for those that go through this, it's still a crushing blow to be dealt while growing your family. Just remember that things are what they are for a reason- even if we don't know what that reason is.