Dogs like to cling to pregnant women because pregnant women have some special smells, such as hormones, progesterone, estrogen, milk fragrance, etc. Humans may not be able to detect it, but dogs can smell it; and dogs will also know it. Pregnant women are relatively weak during pregnancy and want to protect them, so they stick to them all the time.
Tip:
Dogs are very humane animals, so you can keep a dog even if you are pregnant.