A variety of anatomic and physiologic changes occur during pregnancy. In most cases, there is minimal impact on the mother's health. However, there is the possibility that EMS providers will be called to assist a pregnant female.1 Managing the pregnant patient can present unique challenges. Always remember that you are caring for two patients-the mother and the unborn fetus.
The following article provides an overview of the physiologic changes associated with pregnancy, assessment and management of the pregnant patient, examples of pregnancy-related complications, as well as assessment and treatment options to consider when helping a gravid female. Having this background may prove to be invaluable when assessing and managing the pregnant patient, and may even assist in reducing maternal morbidity and mortality.
Anatomical and Physiologic Changes
Following is a brief overview of the anatomic and physiologic changes that occur in the pregnant woman. Table I offers a summary of common OB/GYN terminology.
In a normal pregnancy, the placenta develops in the endometrium-the mucous membrane that lines the uterus. It has several functions, including the exchange of respiratory gases, transport of nutrients between mother and fetus, and hormone production. The umbilical cord connecting the placenta to the fetus consists of one umbilical vein and two arteries and is present from the sixth week of pregnancy through delivery. The vein carries oxygenated blood toward the fetus; the arteries return the blood from the fetus to the mother.2,3
While the placenta provides nutrients to the fetus and assists with the removal of wastes, the amniotic sac, which consists of membranes that cover the fetus, provides protection. The amniotic sac fills with amniotic fluid that is designed to protect the fetus and to provide an environment that is optimal for fetal development. A volume of up to one liter of amniotic fluid is maintained by the fetus's excretion of urine, as well as its swallowing of the amniotic fluid.2,3
Fetal Development & Trimesters
Fetal development begins immediately following implantation of a fertilized egg. The normal duration of pregnancy is 40 weeks from the first day of the mother's last menstrual cycle. Table II provides a summary of fetal development time frames.
Pregnancy is often described in trimesters, with each trimester lasting 13 weeks, or three calendar months. The first trimester is comprised of months one through three, or weeks 1–15; the second trimester consists of months four through six, or weeks 16–27; and the third trimester includes months seven through nine and accounts for weeks 28–40. Pregnancy can also be described in halves: The first half includes weeks 1–20, the second half accounts for weeks 20 through delivery.2,3
Oxygen Delivery to Fetus
Delivery of oxygen to the fetus is dependent on the mother's arterial oxygen content and uterine blood flow. To maximize oxygen delivery, uterine blood flow-normally 2% of total cardiac output in a nonpregnant patient-increases to 18% of cardiac output by the third trimester. Any factor that affects arterial oxygen content (e.g., hypotension, vasoconstriction of the placental bed or uterine contractions) or uterine blood flow will also affect fetal oxygenation. Factors that affect the delivery of oxygen to placenta include the oxygen content of uterine blood, maternal hemoglobin and uterine blood flow.2-9
Maternal system changes