Signs and symptoms which may alert women, and their health care providers, to the possibility of pregnancy include: a missed menstrual period, nausea and/or vomiting, increased frequency of urination, fatigue, breast tenderness, and/or mood changes.
Often, medical providers confirm suspected pregnancy, usually by conducting a pregnancy-related history, performing a urine pregnancy test, and/or conducting a physical examination. In addition, many women use highly sensitive over-the-counter pregnancy tests.
Learning of a positive pregnancy diagnosis, a woman may feel immediate, intense emotion, ranging from complete joy to utter despair. When a woman's reaction is one of confusion or conflicting emotions, she may be unsure of her next steps, and seek information from her medical provider and/or public health practitioner.
Professionals who deliver pregnancy test results and/or Pregnancy Options Counseling should provide each woman with comprehensive information in a sensitive and non-judgmental manner (regardless of the age and life circumstances of the individual) so that she may weigh the range of clinical options and make her own decision.
Stages of Pregnancy
A full-term pregnancy is considered to last 40 weeks from the first day of the pregnant woman's last menstrual period (LMP) prior to fertilization. Pregnancy is generally divided into trimesters:
- First Trimester - the first 12 weeks of pregnancy in which embryonic and early fetal development takes place.
- Second Trimester - the 13-27th weeks of pregnancy.
- Third Trimester - the 28-40th weeks of pregnancy.
Fertilization, the fusion of the male sperm with the female ova in the fallopian tube to form a single cell called the zygote. Once formed, the rapidly dividing zygote travels towards the uterus (which takes about three days). Transport is facilitated by ciliated epithelium (epithelium are hair-like structures that wave actively in one direction) and subtle contractions of the fallopian tube.
When the zygote reaches the uterus it has become a blastocyst (a small cluster of cells) that remains in the uterus for four or five days before it penetrates into the thickened endometrium (uterine lining). This process, called implantation occurs approximately 10 days after fertilization and marks the beginning of the embryonic period (development which occurs during the first eight weeks of pregnancy).
The American College of Obstetricians and Gynecologists (ACOG) defines the beginning of pregnancy at the completion of implantation into the lining of the uterus.
For the first eight weeks post-fertilization, and ten weeks from the last menstrual period (LMP), the cells are termed an "embryo." After eight weeks post-fertilization and ten weeks from LMP until birth, the term changes to "fetus." During the first trimester, the embryo is the most susceptible to environmental influences; during this stage, the majority of organ system formation occurs.
During the early stages of embryonic development, a thin membrane called the amnion develops, which surrounds and protects the embryo. The membrane contains amniotic fluid, which cushions the fetus and helps to maintain even temperature throughout pregnancy.
The outer cells of the embryo form projections, called "villi" that attach themselves to the uterine wall. This attachment becomes the placenta, a vascular spongy structure through which the embryo, and later the developing fetus, derives oxygen, antibodies and nutrients from the maternal blood supply. Waste products also pass from the fetus back to the maternal blood supply through the placenta. The embryo is connected to the placenta by the umbilical cord.
Soon after implantation, the placenta secretes a hormone called HCG (human chorionic gonadotrophin). HCG prevents the disintegration of the corpus luteum, which will secrete large quantities of estrogen and progesterone. Increased estrogen production also causes the enlargement of the uterus, breasts, and external genitalia. Increased progesterone helps to maintain the endometrium, prevents uterine contractions during the pregnancy, and prepares the breasts for lactation.
By the end of the fourth week, all major organ systems begin to form. Primitive nervous system development begins with the neural tube (the beginnings of the brain and the spinal cord). The cardiovascular system also begins to develop. The heart begins beating during the 4th week, and limb buds (which eventually become the arms and legs) also develop by the fourth week. By the end of eight weeks, all major body systems (circulatory, nervous, digestive and urinary systems) continue to develop and function.
- HCG is secreted into the urine of a pregnant woman, and is the basis of most commercial urine pregnancy test kits. Along with history and physical examination, HCG is used to diagnose pregnancy.
- Studies indicate that about 50-70% of neural tube defects (NTDs) could be prevented if women obtained sufficient amounts of folic acid before becoming pregnant and during pregnancy. There is a higher incidence of NTDs among females (60-70% female), and there are ethnic, geographic, and environmental differences.
- Because the neural tube forms in the very early stages of embryonic development, initiating folic acid after pregnancy diagnosis is too late. Women who could become pregnant should get 400 micrograms of synthetic folic acid each day, or eat food enriched with 100% of the daily value of folic acid.
The end of the first trimester marks the beginning of the fetal period (from 9-12 weeks), and is characterized by continued structural growth and development of the major organ systems and the external genital organs.
Exposure or ingestion of environmental or chemical toxins (e.g. x-rays, certain drugs and/or infections, environmental pollutants) can result in congenital malformation, impaired growth or fetal death. The early diagnosis of pregnancy therefore can alert women and their health care providers to avoid exposures to potential teratogens (substances which cause the development of abnormalities in an embryo or fetus).
The second trimester occurs during weeks 13-27 and is marked by accelerated growth, the development of reflex responses and muscular activity. The placenta is fully developed and the brain undergoes the most important period of growth.
The third trimester begins at week 28 and continues until the birth of the baby. All major organ systems continue to grow and mature including the brain, the kidneys and the lungs. By approximately the 36th week, the fetal head may "drop" into the pelvis, a process called lightening. The fetus is considered full-term at >= 37 weeks. It weighs approximately 3000-3600 grams, unless small for gestational age (SGA).
- Gestational age and fetal weight determine infant survival chances if labor begins early. According to the 2002 ACOG Guidelines, survival prior to 24 weeks gestation is extremely rare and the likelihood of survival increases with time. The guidelines note that the survival rates increase from 0% at 21 weeks gestation to 75% at 25 weeks gestation; and from 11% at 401-500 grams to 75% at 701-800 grams birth weight. Long-term follow-up studies are being conducted to assess the degree of increased risk for cognitive and neurological deficit with younger and smaller babies.
- Low birth weight - refers to babies weighing less than 2,500 grams at birth (5 lbs, 8 oz.).
- Very low birth weight - refers to babies weighing less than 1,500 grams or 3-4 lbs. at birth.
- Pre-term labor - refers to the onset of labor before 37 weeks.
- Despite educational and medical interventions geared towards the prevention and arrest of pre-term labor, it still remains a significant clinical problem and leads to high rates of infant mortality and morbidity.
For more information about pre-term infants, visit the March of Dimes website.
The health status of a woman prior to and during pregnancy is critically important for the health and well being of the woman, and for the outcome her pregnancy. However, in the United States and around the world, standards vary.
"Most of the antenatal (prenatal) care models currently in use around the world have not been subjected to rigorous scientific evaluation to determine their effectiveness. Despite a widespread desire to improve maternal care services, this lack of "hard" evidence has impeded the identification of effective interventions and thus the optimal allocation of resources. In developing countries, routinely recommended antenatal care programs are often poorly implemented and clinical visits can be irregular, with long waiting times and poor feedback to the women." WHO Antenatal Care Randomized Trial, 2001.
Comprehensive prenatal care (also know as antenatal care) is designed to:
- Provide baseline health assessments (i.e. blood pressure, Pap smear, height, weight), and screenings for medical conditions that increase pregnancy-related risks (i.e. cardiovascular disease, hypertension, anemia, diabetes, and sexually transmitted infections including HIV, and/or urinary tract infections).
- Identify maternal behaviors that may increase risk (i.e. smoking, poor nutrition, substance use, psychosocial stressors, and unprotected sex), and initiate appropriate treatments.
- Provide genetic counseling.
- Provide health education focused on healthy nutrition/folic acid requirements, exercise, risk reduction, signs and symptoms of pre-term labor and/or other pregnancy complications that require immediate attention.
- Monitor the pregnancy to assure adequate weight gain, fetal growth, fetal heart beat, blood pressure control, assessment of fetal position (later in pregnancy), and assessment to exposure to environmental and infectious agents that can impact pregnancy.
- Identify risk factors for pre-term labor, treat conditions that may cause pre-term labor, and teach women the signs and symptoms of early labor, so that they may seek medical attention promptly.
- Identify maternal health and/or psychosocial factors that will require on-going post-pregnancy care (pregnancy and childbirth may motivate women to address physical and emotional health issues).
- Assess eligibility and provide referral for social welfare and entitlements programs available to the woman and her family.
In many developing countries, prenatal care consists of monitoring weight and blood pressure, measuring the fetal heartbeat, providing a tetanus toxoid immunization, administration of folic acid and iron, syphilis testing (rarely done), and birth planning for potential complications during delivery.