Pregnancy: Terms and Clinical Considerations
Timing of key events
"Gestational age" begins at the date of the last menstrual period.
Conception age, aka, fetal age, begins at the time of conception.
Since conception occurs during the fertile window around ovulation, this is approximately 2 weeks later than the last menstrual period and gestation date (assuming a menstrual cycle of approximately 28 days,
which is unlikely).
Note that, according to "gestational age," a person is already 4 weeks "pregnant" by the time the first menstrual period is missed. However, many people experience light bleeding or spotting as a result of implantation at this 4-week mark, and mistake it for a light period. Thus, a missed period isn't noticed until 8 weeks gestation.
A full-term pregnancy is approximately 40 weeks from the gestation date (last menstrual period).
We use
Naegele's rule to estimate due date: add 9 months + 7 days to the last menstrual period.
Be aware that this rule is a guideline, not a deadline, as gestation length depends on the mother's ethnicity, age, weight, height, timing of ovulation, and other factors.
Trimesters:
The first trimester includes weeks 0-12; fatigue and morning sickness are common in the first trimester.
The second trimester includes weeks 13-28; sensations of fetal movements typically start during this trimester.
The third trimester includes weeks 29-40; this trimester is often marked by dyspnea and discomfort from the enlarged uterus.
A "live birth" indicates the delivery of a neonate (aka, newborn).
Neonatal period lasts 4 weeks post-birth.
Preterm or "early" delivery is birth before 37 weeks
Late term is delivery past 42 weeks. We worry about late term births because it can result in a large fetus with diminished placental capacity.
Embryonic period of development lasts from gestational weeks 2-10 (thus, it begins at the date of conception),
Fetal period lasts from weeks 11 onward.
Perinatal period lasts from 22 weeks gestational age through 1 week post-birth.
Throughout the pregnancy, from diagnosis to delivery, close monitoring for aberrations in fetal development is conducted using a battery of tests and tools.
Pregnancy determination: hCG in urine or blood, ultrasound.
Screening and monitoring: Maternal glucose, fetal heart monitoring, ultrasounds for fetal and uterine development, genetic testing (sampling maternal blood, amniocentesis, chorionic villus sampling), testing for maternal infections.
The death of a conceptus at any gestational age.
20 weeks of gestation is a significant marker: most concepti are lost in the first 20 weeks.
Before 20 weeks of gestation, spontaneous abortion, aka, miscarriage, occurs in up to 20% of confirmed pregnancies (and in up to 50% of all pregnancies, since many concepti are lost before pregnancy is known).
After 20 weeks of gestation, stillbirth, aka, fetal demise, is less common, and includes death before or during delivery (be aware that we are using the CDC definition of fetal demise; WHO defines fetal demise as death at 28 weeks or later).
Top causes of stillbirth include chromosomal abnormalities, placental abruption, maternal hypertension and maternal diabetes.
After 20 weeks of gestation, fetal demise puts the mother at risk of disseminated intravascular coagulation, so removal of the fetal remains is necessary.
Death before the first birthday.
Top causes include birth defects, complications stemming from pre-term delivery, low birth weight, Sudden Infant Death syndrome (SIDS), and injuries.
In the United States, the infant mortality rate is 5.4 deaths per 1000 live births.
Infant mortality in the US is much higher than other developed countries, and the rate is almost doubled in US Black populations (10.4 deaths per 1000 live births).
Perinatal mortality rates are influenced by maternal health (before, during, and after pregnancy), maternal age, and sociodemographic factors.
Defined as maternal death during pregnancy or within 42 days of pregnancy termination (including termination via live birth).
The United States had an average of 23.8 deaths/100,000 live births in 2020; this is the highest rate among developed countries.
Be aware that the maternal mortality rate is much higher among Black patients, at about 43 deaths per 100,000 live births, and is also elevated among poorer populations in the U.S.
Top causes of maternal mortality include severe bleeding/hemorrhaging, infections, and hypertension. Mental health conditions, including overdose and suicide, also contribute to high maternal mortality.
Key Pregnancy Complications
Hypertension is one of the most common complications and a top cause of maternal death.
Gestational hypertension is new-onset hypertension in pregnancy, but without features of pre-eclampsia.
Pre-eclampsia is characterized by hypertension with proteinuria; it is thought to be caused by abnormal vascular development in the placental leading to underperfusion, hypoxia, and fetal growth restriction. Signs to look out for include epigastric pain, vomiting, frontal headaches, and blurred vision.
Pre-eclampsia can be with or without severe features; severe features include worse hypertension and proteinuria and/or other features, including hepatic or renal dysfunction, pulmonary edema, thrombocytopenia, and cerebral or visual disturbances.
Eclampsia is characterized by grand-mal seizures in a pre-eclamptic patient; we can remember this by knowing that "eclampsia" means "lightening."
HELLP is a syndrome characterized by Hemolysis, Elevated Liver enzymes, and Low Platelets in the final weeks of pregnancy or shortly after delivery, most often in patients who are or were pre-eclamptic. It is associated with high maternal and perinatal death rates.
Venous thromboembolic events are another top cause of maternal mortality. Recall
Virchow's triangle of thromboembolism formation: hypercoagulable state with venous stasis and damage. Pregnancy is intrinsically associated with all three, and many patients have additional risk factors (smoking, advanced age, etc.).
Placental disorders
Placenta previa: the placenta sits low in the uterus, covering the opening of the cervix.
Abnormally invasive placenta: the placenta invades the walls of the uterus. Learn more about
placental disorders.
Infection
TORCHeS infections: Toxoplasmosis, Other: Varicella-Zoster Virus, Listeriosis, etc., Rubella, Cytomegalovirus, Herpes Simplex Virus and HIV, and Syphilis.
Other infections that can complicate a pregnancy include:
Group B Streptococcus,
bacterial vaginosis,
urinary tract infections,
sexually transmitted diseases, and COVID-19.
Gestational diabetes
New-onset diabetes that can lead to macrosomia and hypoglycemia in the neonate.
Ectopic pregnancies
Occur when a conceptus implants outside the uterus, usually in the uterine tube.
Ectopic pregnancies are not viable, but their growth can damage the maternal organs and cause life-threatening loss of blood. Patients may experience amenorrhea or other signs of pregnancy, vaginal bleeding, and abdominopelvic pain.
Pharmacological complications
Arise from the altered pharmacokinetics and pharmacodynamics of pregnancy, but pregnancy-specific instructions are lacking for most drugs.
For references, please see full tutorial.
