Obstetrics

Obstetrics is the surgical specialty dealing with the care of women and their children during pregnancy, childbirth and the puerperium. Midwifery is the non-medical equivalent. Veterinary obstetrics is the same concept for veterinary medicine

Antenatal care
In obstetric practice, an obstetrician or midwife sees a pregnant woman on a regular basis to check the progress of the pregnancy, to verify the absence of ex-novo disease, to monitor the state of preexisting disease and its possible effect on the ongoing pregnancy. A woman's schedule of antenatal appointment varies according to the presence of risk factors, such as diabetes, and local resources. Some of the clinically and statistically more important risk factors that must be systematically excluded, especially in advancing pregnancy, are pre-eclampsia, abnormal placentation, abnormal fetal presentation and intrauterine growth restriction. For example, to identify pre-eclampsia, blood-pressure and albuminuria (level of urine protein) are checked at every opportunity. Placenta praevia must be excluded (PP = low lying placenta that, at least partially, obstructs the birth canal and therefore warrants elective caesarean delivery); this can only be achieved with the use of an ultrasound scan. However, early placenta praevia is not alarming; this is because as the uterus grows along the pregnancy, the placenta may still move away. A placenta praevia is of clinical significance as from the 28th week of gestation. The current management includes a caesarean section. The type of caesarean section is determined by the position (anterior or posterior) of the placenta. In late pregnancy fetal presentation must be established: cephalic presentation (head first) is the norm but the fetus may present feet-first or buttocks-first (breech), side-on (transverse), or at an angle

Maternal physiology
During pregnancy, the woman undergoes many physiological changes, which are entirely normal, including cardiovascular, hematologic, metabolic, renal and respiratory changes that become very important in the event of complications.

Cardiovascular
The woman is the sole provider of nourishment for the embryo and later, the fetus, and so her plasma and blood volume slowly increase by 40-50% over the course of the pregnancy to accommodate the changes.[1] This results in overall vasodilation, an increase in heart rate (15 beats/min more than usual), stroke volume, and cardiac output. Cardiac output increases by about 50%, mostly during the first trimester. The systemic vascular resistance also drops due to the smooth muscle relaxation caused by elevated progesterone, leading to a fall in blood pressure. Diastolic blood pressure consequently decreases between 12–26 weeks, and increases again to prepregnancy levels by 36 weeks. If the blood pressure remains abnormal beyond 36 weeks, the woman should be investigated for pre-eclampsia, a condition that precedes eclampsia.

Endocrine
Pregnant women experience adjustments in their endocrine system. These adjustments include an increase in her estrogen levels; which is mainly produced by the placenta and is associated with fetal well–being. Women also experience increased human chorionic gonadotropin (ß-hCG); which is produced by the placenta. This maintains progesterone production by the corpus luteum. Additionally, human placental lactogen (hPL) is produced by the placenta, ensuring nutrient supply to the fetus. This also causes lipolysis and is an insulin antagonist, which is a diabetogenic effect. Additionally, there is increased prolactin, increased alkaline phosphatase, and increased progesterone production, first by corpus luteum and later by the placenta, whose main course of action is to relax smooth muscle.

Hematology
During pregnancy the plasma volume increases by 50% and the red blood cell volume increases only by 20-30%.[1] Consequently, the hematocrit decreases on lab value, however this is not a true decrease in hematocrit, but rather due to the dilution. The white blood cell count increases and may peak at over 20 mg/mL in stressful conditions. Conversely, there is a decrease in platelet concentration to a minimal normal values of 100-150 mil/mL. A pregnant woman will also become hypercoagulable, leading to increased risk for developing blood clots and embolisms, due to increased liver production of coagulation factors, mainly fibrinogen and factor VIII (this hypercoagulable state along with the decreased ambulation causes an increased risk of both DVT and PE). Women are at highest risk for developing clots, or thrombi, during the weeks following labor. Clots usually develop in the left leg or the left iliac venous system. The left side is most afflicted because the left iliac vein is crossed by the right iliac artery. The increased flow in the right iliac artery after birth compresses the left iliac vein leading to an increased risk for thrombosis (clotting) which is exacerbated by the aforementioned lack of ambulation following delivery. Both underlying thrombophilia and cesarean section can further increase these risks. Edema, or swelling, of the feet is common during pregnancy, partly because the enlarging uterus compresses veins and lymphatic drainage from the legs.