Seafood in moderation is fine, but there are certain kinds of fish that should be avoided during pregnancy. Mackerel, swordfish and shark are very rich in mercury, an element that should only be taken in very small amounts while pregnant, as it has been linked to birth defects.

A four-month-old baby should recognize toys, particularly ones that rattle, make fun noises, or are bright in color. They may reach for toys, shake toys, or swing at dangling toys.

The amount of blood in your body will rise dramatically during pregnancy. By the time you give birth, you'll have about 50 percent more blood circulating than usual.

The placenta is responsible for working as a trading post between the mother’s and the baby’s blood supply. Small blood vessels carrying the fetal blood run through the placenta, which is full of maternal blood. Nutrients and oxygen from the mother’s blood are transferred to the fetal blood, while waste products are transferred from the fetal blood to the maternal blood, without the two blood supplies mixing.

Functional hypothalamic amenorrhea (FHA) relates to excessive physical or emotional stress that results in amenorrhea (absent periods).

Prolactin is a hormone that plays a role in fertility by inhibiting follicle stimulating hormone (FSH) and gonadotropin-releasing hormone (GnRH), the hormones that trigger ovulation and allow eggs to develop and mature.