To confirm what other Lactnetters have said:

"The scalp contains approximately 100,000 hair follicles. Hair fibers in
each follicle independently cycle through three growth stages:  anagen,
catagen, and telogen.  The anagen or growth stage lasts for 4 to 6 years
and is characterized by intense metabolic activity.  In this stage hair
grows an average of 0.34 mm/day.  Catagen is a transitional stage lasting
several weeks.  During this stage metabolic activity and growth slow as the
hair bulb is retracted upward into the follicle.  Growth of the hair fiber
stops during telogen (resting stage). Eventually a new hair bulb begins
growing, which ejects the previous hair.  Normally about 80% of hair
follicles are in the anagen stage and 15 to 20% of hair fibers are in the
telogen stage, with about 100 hairs shed per day.
"Under the influence of estrogen during pregnancy, the rate of hair growth
slows and the anagen stage is prolonged.  This results in an increased
number of anagen hairs and a decrease in telogen hairs to less than 10%
during the second and third trimesters.  During the postpartum period these
anagen hairs enter catagen and then telogen and are shed.  Since there are
more anagen hairs (and thus telogen hairs) than usual, most postpartum
women experience an increased hair loss begining 4 to 20 weeks following
delivery.  During this time 30 to 35% of the hairs may enter telogen.
Generally, complete regrowth occurs by 6 to 15 months, although the hair
may be less abundant than prior to pregnancy.  "Telogen effluvium" is the
term used to describe the rapid transition of hair follicles into the
telogen stage following delivery, surgery, or severe emotional or physical
stress."

Blackburn, Susan Tucker and Loper, Donna Lee, "Maternal, Fetal, and
Neonatal Physiology:  A Clinical Perspective," W.B. Saunders: Philadelphia,
1992: pp. 497-498 (6 ref. to this section).

[log in to unmask] (Arly Helm, MS, CLE, IBCLC)