Heredity and habit.
Physical and emotional causes.
The onset of labor probably is not purely accidental, and yet it is so inconstant in appearance and so indifferently early or late, that it has every appearance of being an affair of chance. The time when labor will come on is highly speculative in general, but the phenomenon is preceded by certain definite symptoms:
The lightening.
False pains.
Show.
Rupture of membranes.
The pains.
Lightening.—About two weeks before labor, especially in a primipara, the uterus and the head sometimes descend into the pelvis. The body of the child falls forward and the abdomen protrudes, the stomach is flatter, the patient breathes easier and feels, as she says, “lighter.” But walking is more difficult, the bladder is stimulated to frequent evacuations and the rectum is compressed.
This occurrence is a premonitory sign of labor, and also favorable inasmuch as it demonstrates that this particular head is not too large to pass this particular pelvis.