Interesting phenomenon

I was told that my mother became pregnant with me because her best friend was pregnant. My mother was 1 month behind her best friend. I've noticed this happens a lot. My step-daughter gets pregnant, and shortly after, her cousin, who is more like a sister, is also pregnant. I've been scouring the Baptismal records for New Mexico's Catholic Churches looking for ancestors. I've noticed that very often I'll find females related to each other with children being baptized within days of each other. I've noticed this for sisters, sister-in-laws, and even mothers and their daughters. I've always found this fascinating, but after finding this phenomenon happening consistently through my genealogical resources, I'm really amazed.

My SIL got pregnant with my nephew and, 2 months later, my cousin was pregnant. Even more than that, I got pregnant and withing two months BOTH of my female cousins on my dad's side AND my best friend got pregnant. The birthdates are all within 2 months of each other (my cousin's had theirs just 6 days apart).