**2. Physiology of the puerperium**

### **2.1 Uterus**

The uterus weighs approximately 1000 gm and has a volume of 5 L immediately after delivery, compared with its non pregnant weight of approximately 70 g m and 5–10 ml.

Just after delivery, the height of the uterine fundus is halfway between the pubic symphysis and the umbilicus. It happens because of the delivery of the fetus, placenta and amniotic fluid. Also there is loss of hormonal stimulation.

The height of the fundus just after delivery is 13.5 cm above the symphysis pubis. The level remains constantfor first 24 hours. After that, there is a steady decrease in height by 1.25 cm in 24 hours, resulting in uterus so that by the end of 2nd week the uterus becomes a pelvic organ. The rate of involution thereafter slows down getting back the uterus to normal size in 6 weeks. Just after delivery, due to the rapidly decreasing endometrial surface that is attached to the placenta, placenta gets sheared from the decidual layer. The average diameter of the placenta attached to the deciduas is 18 cm; which goes down to 9 cm in the immediate postpartum period.

For the first 3 days after delivery, the placental site is infiltrated with granulocytes and mononuclear cells. It is a reactionary change that extends into the endometrium and superficial myometrium as well.

By the 7th day, the regeneration of endometrial glands is evident, and they often appear atypical with irregular chromatin patterns, enlarged nuclei, pleomorphism and increased cytoplasm.

By the end ofthe first week, regeneration of the endometrial stroma is also evident, and mitotic figures are noted in gland epithelium. By postpartum day 16, the endometrium gets fully restored.

Just after birth, hemostasis is achieved by arterial smooth muscle contraction and compression of vessels by the involuting uterine muscle. In the first 8 days, vessels in the placental site are characterized by thrombosis, hyalinization. Endophlebitis in the veins and hyalinization and obliterativefibrinoid endarteritis in the arteries are notable findings.

The postpartum uterine discharge, or lochia, begins as a flow of blood that lasts several hours, then rapidly diminishes to a reddish brown discharge through the third or fourth day postpartum.

The post partum discharge is termed lochia and it contains erythrocytes, shredded decidua, epithelial cells and bacteria. For the first few days after delivery, it is known as lochia rubra. After 3 or 4 days, lochia becomes progressively pale in color and is known as lochia serosa. Then at around 10th day, because of an admixture of leukocytes and reduced fluid content, lochia assumes a white or yellow-white color known as lochia alba. The average duration of puerperial lochial discharge is from 24 to 36 days [1].

Breastfeeding or the use of oral contraceptive agents does not affect the duration of lochia. The cervical os contracts slowly, and for a few days just after labor, it readily admits two fingers. Gradually, this opening narrows and the cervix thickens with reformation of endocervical canal in a week. The external os never resumes its pre gravid appearance. It remains somewhat wider with the ectocervical depressions getting permanent at the site of lacerations.

#### **2.2 Birth canal**

The vagina and the introitus gradually reduce in size but hardly regain the nulliparous size and shape. Rugae start appearing by the third week but are less prominent. The hymen is represented by several small tissue tags of tissue that form the myrtiform caruncles.

After delivery, the vaginal epithelium reflects the hypoestrogenic state, and it stops proliferating until 4 to 6 weeks. Some damage to the pelvic floor may be inevitable, and parturition predisposes to urinary incontinence and pelvic organ prolapse.
