How Breasts Change During Pregnancy

April 17, 2011— -- Breasts are good for much more than creating cleavage -- they're complex physiological structures. At no other time is this more evident than when you're pregnant and nursing. For instance, did you know lactating breasts can swell by more than a pound? Here is a detailed look at the changes your mammary machinery undergoes during each phase of pregnancy.

First Trimester

The areolae take on a darker hue. A deeper nipple color might make it easier later for the newborn to spot his or her food source.

In preparation for the coming feeding frenzy, a flood of hormones stimulates the growth and expansion of the breasts' milk-producing lobules.

Second Trimester

Breasts begin producing and storing a type of milk called colostrum, a thick, yellowish substance that will feed the baby for its first few days.

By week 16, the breasts are ready to dispense food. To increase a preemie's chance of survival, milk at this stage is higher in protein, iron, sodium, fat, and anti-infective properties.

At 24 weeks, blood flow to the breasts doubles--and will hold steady until birth--to support the ongoing production of milk.

Third Trimester

Tiny milk-making cells inside the alveoli begin to multiply; they'll work on overdrive until they're full of colostrum.

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