Back pain Braxton Hicks contractions. Occasional, irregular, and often painless contractions that occur several times per day. Common complaint in advancing pregnancy. Caused by compression of the inferior vena cava and pelvic veins by the uterus leads to increased hydrostatic pressure in lower extremities. A common complaint, caused by increased intravascular volume, elevated glomerular filtration rate , and compression of the bladder by the expanding uterus.
Urinary tract infection  Varicose veins. Common complaint caused by relaxation of the venous smooth muscle and increased intravascular pressure. Swollen veins at or inside the anal area. Caused by impaired venous return, straining associated with constipation, or increased intra-abdominal pressure in later pregnancy. Chronology The chronology of pregnancy is, unless otherwise specified, generally given as gestational age , where the starting point is the woman's last normal menstrual period LMP , or the corresponding age of the gestation as estimated by a more accurate method if available.
Sometimes, timing may also use the fertilization age which is the age of the embryo. Start of gestational age According to American Congress of Obstetricians and Gynecologists , the main methods to calculate gestational age are: Early obstetric ultrasound , comparing the size of an embryo or fetus to that of a reference group of pregnancies of known gestational age such as calculated from last menstrual periods , and using the mean gestational age of other embryos or fetuses of the same size.
If the gestational age as calculated from an early ultrasound is contradictory to the one calculated directly from the last menstrual period, it is still the one from the early ultrasound that is used for the rest of the pregnancy. Estimated date of confinement Due date estimation basically follows two steps: Determination of which time point is to be used as origin for gestational age , as described in section above. Adding the estimated gestational age at childbirth to the above time point.
Childbirth on average occurs at a gestational age of days 40 weeks , which is therefore often used as a standard estimation for individual pregnancies. Naegele's rule is a standard way of calculating the due date for a pregnancy when assuming a gestational age of days at childbirth. The rule estimates the expected date of delivery EDD by adding a year, subtracting three months, and adding seven days to the origin of gestational age. Alternatively there are mobile apps , which essentially always give consistent estimations compared to each other and correct for leap year , while pregnancy wheels made of paper can differ from each other by 7 days and generally do not correct for leap year.
A study of singleton live births came to the result that childbirth has a standard deviation of 14 days when gestational age is estimated by first trimester ultrasound , and 16 days when estimated directly by last menstrual period. Human fertilization Fertilization and implantation in humans Through an interplay of hormones that includes follicle stimulating hormone that stimulates folliculogenesis and oogenesis creates a mature egg cell , the female gamete.
Fertilization is the event where the egg cell fuses with the male gamete, spermatozoon. After the point of fertilization, the fused product of the female and male gamete is referred to as a zygote or fertilized egg. The fusion of male and female gametes usually occurs following the act of sexual intercourse. Pregnancy rates for sexual intercourse are highest during the menstrual cycle time from some 5 days before until 1 to 2 days after ovulation.
Fertilization conception is sometimes used as the initiation of pregnancy, with the derived age being termed fertilization age. Fertilization usually occurs about two weeks before the next expected menstrual period. A third point in time is also considered by some people to be the true beginning of a pregnancy: This is time of implantation, when the future fetus attaches to the lining of the uterus.
This is about a week to ten days after fertilization. Development of embryo and fetus The initial stages of human embryogenesis The sperm and the egg cell, which has been released from one of the female's two ovaries , unite in one of the two fallopian tubes. The fertilized egg, known as a zygote , then moves toward the uterus, a journey that can take up to a week to complete. Cell division begins approximately 24 to 36 hours after the male and female cells unite. Cell division continues at a rapid rate and the cells then develop into what is known as a blastocyst.
The blastocyst arrives at the uterus and attaches to the uterine wall, a process known as implantation. The development of the mass of cells that will become the infant is called embryogenesis during the first approximately ten weeks of gestation.
During this time, cells begin to differentiate into the various body systems. The basic outlines of the organ, body, and nervous systems are established. By the end of the embryonic stage, the beginnings of features such as fingers, eyes, mouth, and ears become visible.
Also during this time, there is development of structures important to the support of the embryo, including the placenta and umbilical cord. The placenta connects the developing embryo to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. The umbilical cord is the connecting cord from the embryo or fetus to the placenta. After about ten weeks of gestational age, the embryo becomes known as a fetus.
At the beginning of the fetal stage, the risk of miscarriage decreases sharply. Sex organs begin to appear during the third month of gestation. The fetus continues to grow in both weight and length, although the majority of the physical growth occurs in the last weeks of pregnancy. Electrical brain activity is first detected between the fifth and sixth week of gestation. It is considered primitive neural activity rather than the beginning of conscious thought.
Synapses begin forming at 17 weeks, and begin to multiply quickly at week 28 until 3 to 4 months after birth. Gestational age of 6 weeks. Fetus at 8 weeks after fertilization. Gestational age of 10 weeks.
Fetus at 18 weeks after fertilization. Gestational age of 20 weeks. Fetus at 38 weeks after fertilization. Gestational age of 40 weeks. Relative size in 1st month simplified illustration Relative size in 3rd month simplified illustration Relative size in 5th month simplified illustration Relative size in 9th month simplified illustration Maternal changes Main article: Maternal physiological changes in pregnancy Breast changes as seen during pregnancy.
The areolae are larger and darker. During pregnancy, the woman undergoes many physiological changes, which are entirely normal, including behavioral , cardiovascular , hematologic , metabolic , renal , and respiratory changes.
Increases in blood sugar, breathing, and cardiac output are all required. Levels of progesterone and oestrogens rise continually throughout pregnancy, suppressing the hypothalamic axis and therefore also the menstrual cycle.
The fetus is genetically different from the woman and can be viewed as an unusually successful allograft. Many symptoms and discomforts of pregnancy like nausea and tender breasts appear in the first trimester. Although the breasts have been developing internally since the beginning of the pregnancy, most of the visible changes appear after this point.
Weeks 13 to 28 of the pregnancy are called the second trimester. Most women feel more energized in this period, and begin to put on weight as the symptoms of morning sickness subside and eventually fade away. The uterus, the muscular organ that holds the developing fetus, can expand up to 20 times its normal size during pregnancy. Although the fetus begins to move during the first trimester, it is not until the second trimester that movement, often referred to as " quickening ", can be felt.
This typically happens in the fourth month, more specifically in the 20th to 21st week, or by the 19th week if the woman has been pregnant before. It is common for some women not to feel the fetus move until much later. During the second trimester, most women begin to wear maternity clothes.
Third trimester Pregnant woman in third trimester of pregnancy last month The uterus expands making up a larger and larger portion of the woman's abdomen. At left anterior view with months labeled, at right lateral view labeling the last 4 weeks.
During the final stages of gestation before childbirth the fetus and uterus will drop to a lower position. Final weight gain takes place, which is the most weight gain throughout the pregnancy. The woman's abdomen will transform in shape as it drops due to the fetus turning in a downward position ready for birth. During the second trimester, the woman's abdomen would have been upright, whereas in the third trimester it will drop down low.
The fetus moves regularly, and is felt by the woman. Fetal movement can become strong and be disruptive to the woman. The woman's navel will sometimes become convex, "popping" out, due to the expanding abdomen.
Head engagement , where the fetal head descends into cephalic presentation , relieves pressure on the upper abdomen with renewed ease in breathing. It also severely reduces bladder capacity, and increases pressure on the pelvic floor and the rectum.
It is also during the third trimester that maternal activity and sleep positions may affect fetal development due to restricted blood flow. For instance, the enlarged uterus may impede blood flow by compressing the vena cava when lying flat, which is relieved by lying on the left side.
Childbirth Childbirth, referred to as labor and delivery in the medical field, is the process whereby an infant is born. While childbirth is widely experienced as painful, some women do report painless labours, while others find that concentrating on the birth helps to quicken labour and lessen the sensations.
Most births are successful vaginal births, but sometimes complications arise and a woman may undergo a cesarean section. During the time immediately after birth, both the mother and the baby are hormonally cued to bond, the mother through the release of oxytocin , a hormone also released during breastfeeding.
Studies show that skin-to-skin contact between a mother and her newborn immediately after birth is beneficial for both the mother and baby. A review done by the World Health Organization found that skin-to-skin contact between mothers and babies after birth reduces crying, improves mother—infant interaction, and helps mothers to breastfeed successfully. They recommend that neonates be allowed to bond with the mother during their first two hours after birth, the period that they tend to be more alert than in the following hours of early life.