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The Anatomy of Obstetrics Kurt Kauffman, MD, FACOG Objectives: Describe the muscular, neurologic and vascular anatomy of the pelvis and vulva Describe the anatomic changes in the woman caused by normal physiologic adaptation to pregnancy Describe the anatomic changes that occur during the intrapartum period Describe the anatomic changes that occur during the puerperium, such as alterations in the breast and uterine involution Pelvic anatomy - muscular Pelvic blood supply Internal illiac artery Anterior branch Obturator artery Superior vesical artery Uterine artery Middle vesical artery Internal pudendal artery Posterior branch Illiolumbar artery Lateral sacral artery Anterior gluteal artery Vulva Labia Majora Labia Minora Clitorus Vestibule Urethral meatus Vaginal introitus Perineum Vulvar Cutaneous Innervation Anatomic changes caused by normal physiologic adaptation to pregnancy Abdominal wall Pelvic organs Breasts Rectus muscles Pelvic organs Uterus enlarges to about 5 Liters total size (including all contents (12 lbs) Uterine muscle Fetus Placenta Fluids Vagina lengthens Round ligaments lengthens Broad ligament stretches (venous plexus engorges) Uterine size and gestational age Pudendal Nerve Controls: External anal sphincter External Urethral sphincter Clitoral erection & Orgasm Posterior perineum sensation Vaginal/Labial changes with pregnancy Increased vascularity Varicosities Unilateral or bilateral – may be quite tender May need supportive garment Enlargement Breast Changes with Pregnancy After conception: Breast become swollen/tender Nipples are more sensitive/tingle Areola/nipple become darker by 12 weeks post conception Ductal, alveolar, and myoepithelial elements all undergo marked hyperplasia. Ductal proliferation is predominantly controlled by estrogen, but acinar differentiation is a progesterone effect facilitated by estrogen. Pregnancy changes in the Breast Anatomic changes during the intrapartum period Dilation of the cervix Thinning/effacement Descent of the fetal head into the vagina Dilation of the vagina as the fetal head descends Dilation of the introitus/vulva as the baby crowns Separation of the placenta after the baby is delivered Lengthening of the cord, bleeding Injury/stretching of nerves to pelvis Perineum/bladder (Pudendal & vesical plexes/hypogastric) Anatomic changes that occur during the puerperium Involution (pelvic organs) Starts immediately post delivery of the placenta Lasts approximately 6 weeks Decrease in estrogen and progesterone aids in involution Breast Changes Post partum involution Uterus starts immediate involution. Contractions immediately decrease blood flow which decreased blood loss and helps with involution Uterine muscles atrophy quickly at first and then continue for 6 weeks Uterus weighs around 900 grams immediately PP – but only 50 – 60 grams at 6 weeks PP Vagina also involutes, but slower Tubes, ligaments and vulvar muscles also involute and return to near pre delivery size Involution of Endometrium Endometrium necrosis and sloughs off Placental implantation site thrombosis over Basal layer is source of new endometrium Placental implantation site first shrinks in diameter, then is exfoliated by undermining of site with new endometrium Involution of Vagina Slower to involute (takes 4 to 8 weeks) Regains tone, but never back to virginal state Mucosa remains delicate for few weeks Rugae partially reappear at 3rd week PP Introitus also remains larger than virginal state Breast changes after delivery Mammary tissue becomes secretive with the abrupt falling of estrogen and progesterone with delivery Lactogenesis requires 2-5 days (maturation of acinar epithelium in breast) Once lactogenesis occurs completely, hormones estrogen and progesterone have little effect on production. References Netter, F., Atlas of Human Anatomy Williams Obstetrics, 23rd edition Gabbe, G.G., et al, Obstetrics Normal and Problem Pregnancies. Fourth edition. www.healthcare.phillips.com