Hey ladies! Did any of you suspect you were pregnant with twins/multiples before your first scan? If so, what made you suspicious?
I'm just curious. My Dad and my maternal grandfather were both fraternal twins and I'm pregnant with my first so I can't help but wonder? Thanks ladies!
Of the factors that influence multiple birth, there is only one that could be identified as genetic or explained by family history: hyper ovulation. Hyper ovulation is the tendency to release multiple eggs during ovulation, increasing the chances of conceiving dizygotic (or fraternal) twins. So, in families where the women have a gene for hyperovulation, genetics would sufficiently explain an increased presence of fraternal twins.
However, only women ovulate. While men can carry the gene and pass it on to their daughters, a family history of twins doesn't make them any more likely to have twins themselves. Fraternal twins "run in families" if she inherits the gene for hyper ovulation.
If you consider the influence of genetic hyper ovulation, this pattern could appear in families depending on whether their children were sons or daughters.
Generation 1: Grandma
Grandma has the gene for hyperovulation. She & Grandpa have fraternal boy twins, Rob and Bob
Generation 2: Rob & Bob
While Grandma's sons may carry the gene for hyperovulation, they do not ovulate. They will not have twins (excluding other factors). However, they each have a daughter.
Generation 3: Molly & Polly
Molly and Polly, cousins, inherit the gene for hyperovulation from their fathers. They each have a set of twins.
You can see how this example makes it appear that twins skip a generation in families. The pattern is influenced by whether the inheritor of the hyper ovulation gene is male or female.