Dynamics of uterine contraction and healing
Immediately after the birth of the placenta, the uterus is a spherical organ whose fundus is palpable 15–18 cm above the pubic symphysis. Due to the overstretched ligamentous apparatus, it has high mobility.
The reduction in the organ's mass occurs rapidly due to the tonic contraction of muscle fibers, which leads to vascular compression, partial obliteration, and atrophy of some myocytes:
- Immediately after delivery — 1000 g
- End of the 1st week — 500 g
- End of the 2nd week — 325 g
- End of the 3rd week — 250 g
- By the 6th–8th week — 50 g (the norm for a non-pregnant woman)
The inner surface of the uterus after childbirth is a wound. The deepest lesions are localized in the area of the placental site, where thrombosed vessels are gaping. The cleansing of the cavity from blood clots and decidual remnants occurs from the 4th to the 10th day thanks to the activity of proteolytic enzymes. Endometrial epithelization is generally completed by the 10th–12th day, while healing of the placental site requires more time and ends only by the end of the 3rd week.
Formation of the protective barrier
To prevent infection from penetrating the uterine wall, a specific granulation wall forms in the subepithelial layers on the 2nd–4th day. It is a zone of pronounced small-cell infiltration. Bacteria entering the uterine cavity are destroyed by macrophages, enzymes, and biologically active substances. As the organ heals and involutes, this protective barrier gradually resolves.
Evolution of postpartum discharge (lochia)
The wound secretion released from the uterine cavity is called lochia (lochia). It has an alkaline reaction and a characteristic stale odor. The nature of the discharge changes predictably as the endometrium heals:
- First 2–3 days: discharge consists primarily of blood — lochia rubra (bloody).
- From the 3rd–4th day to the end of the 1st week: the secretion becomes lighter, serosanguineous — lochia serosa.
- From the 10th day: the discharge acquires a yellowish-white tint due to a large number of leukocytes — lochia alba.
- From the 3rd week: thick mucus from the cervical canal is added to the secretion.
Normally, the release of lochia completely ceases by the 5th–6th week of the postpartum period.
Changes in the cervix, vagina, and appendages
Cervical involution proceeds significantly slower than that of the uterine body. 10–12 hours after delivery, the cervical canal has a funnel shape, and the internal os admits 2–3 fingers (5–6 cm in diameter). By the 10th day, the internal os closes, but the final formation of the cervix is completed only by the 13th week. Due to lateral tears during childbirth, the external os remains a transverse slit (in nulliparous women it is pinpoint), and the cervix itself changes its shape from conical to cylindrical.
The vagina gradually narrows in the first weeks, and the edema and hyperemia of the walls subside. The remnants of the ruptured hymen scar, forming myrtiform caruncles (carunculae myrtiformes).
The fallopian tubes return to their pre-pregnancy state in 2 weeks (edema subsides, blood flow normalizes). Maturation of new follicles begins in the ovaries. It is important to remember that although high levels of prolactin during lactation inhibit ovulation, a new pregnancy during breastfeeding is absolutely possible.
Extragenital changes
The postpartum period is accompanied by the restructuring of all body systems:
- Hemodynamics: due to the drop in intra-abdominal pressure, extracellular fluid rushes into the vascular bed, increasing circulating blood volume (CBV). Immediately after delivery, tachycardia, an increase in cardiac output, and a transient rise in blood pressure by 5–6% are observed.
- Urinary system: urinary bladder hypotonia is often observed (especially after prolonged labor or with a large fetus), leading to an absence of urges and difficult urination. Glomerular filtration recovers by the 8th week, and renal blood flow by the 5th–6th week.
- Gastrointestinal tract: atonia of the intestinal smooth muscle is characteristic, provoking constipation. In 80% of postpartum women, hemorrhoids manifest or exacerbate, carrying a risk of infringement.
To memorize the stages of lochia, use the "R-S-Y" rule (Red, Serous, Yellow): Rubra (bloody) — first 3 days, Serosa (serosanguineous) — until the end of the 1st week, Yellowish-white (alba) — from the 10th day.
Class and exam questions
Why does the uterus lose mass so quickly after childbirth?
The main mechanism is the constant tonic contraction of the myometrium. It leads to a sharp decrease in blood supply, hypotrophy and partial atrophy of muscle fibers, as well as the obliteration of most vessels.
How does the uterus defend against infections in the postpartum period?
On the 2nd–4th day, a granulation wall of small-cell infiltration forms in the subepithelial layers. It serves as a reliable barrier, while proteolytic enzymes and macrophages destroy microorganisms directly within the uterine cavity.
Is it possible to become pregnant during lactation before the return of the first menstruation?
Yes. Despite the fact that the hormone prolactin inhibits ovulation, follicle maturation in the ovaries continues. The onset of ovulation and pregnancy against the background of active breastfeeding is not excluded.
How does the shape of the cervix change in parous women?
Due to tissue overstretching and micro-tears during childbirth, the cervix becomes cylindrical (it was conical before delivery). The external os thus acquires the shape of a transverse slit instead of a pinpoint one.
What else to study on this topic
- Hemodynamic shifts immediately after delivery: causes of tachycardia and transient hypertension.
- Pathogenesis and clinical manifestations of urinary bladder hypotonia in postpartum women.
- Mechanisms of granulation wall formation and local immunity of the uterine cavity.
- Prevention of thromboembolic complications against the background of physiological postpartum hypercoagulation.
- Features of placental site healing and risks of uterine subinvolution.
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