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Duration of Pregnancy

The expected date of delivery (EDD) is 40 weeks counting from the first day of the last menstrual period (LMP), and birth usually occurs between 37 and 42 weeks. Though pregnancy begins at implantation, it is more convenient to date from the first day of a woman's last menstrual period, or from the date of conception if known. Starting from one of these dates, the expected date of delivery can be calculated using the Naegele's rule for estimating date of delivery. A more sophisticated algorithm takes into account other variables, such as whether this is the first or subsequent child (i.e., pregnant woman is a primip or a multip, respectively), ethnicity, parental age, length of menstrual cycle, and menstrual regularity.

Pregnancy Overview

Physiology of Pregnancy
Diagnosis of Pregnancy
Duration of Pregnancy
Nutritional Care in Pregnancy


Pregnancy is considered "at term" when gestation attains 37 complete weeks but is less than 42 (between 259 and 294 days since LMP). Events before completion of 37 weeks (259 days) are considered preterm; from week 42 (294 days) events are considered postterm. When a pregnancy exceeds 42 weeks (294 days), the risk of complications for both the woman and the fetus increases significantly, as such, obstetricians usually prefer to induce labour, in an uncomplicated pregnancy, at some stage between 41 and 42 weeks.

Accurate dating of pregnancy is important, because it is used in calculating the results of various prenatal tests (for example, in the triple test). A decision may be made to induce labour if a fetus is perceived to be overdue. Furthermore, if LMP and ultrasound dating predict different respective due dates, with the latter being later, this might signify slowed fetal growth and therefore require closer review.

 Menstrual Period

The menstrual cycle is the scientific term for the physiological changes that can occur in fertile female humans. Overt menstruation (where there is blood flow from the uterus through the vagina) occurs in humans.
The menstrual cycle, under the control of the endocrine system, is necessary for reproduction. It is commonly divided into three phases: the follicular phase, ovulation, and the luteal phase; although some sources use a different set of phases: menstruation, proliferative phase, and secretory phase. Menstrual cycles are counted from the first day of menstrual bleeding. Hormonal contraception interferes with the normal hormonal changes with the aim of preventing reproduction.

Stimulated by gradually increasing amounts of estrogen in the follicular phase, discharges of blood (menses) slow then stop, and the lining of the uterus thickens. Follicles in the ovary begin developing under the influence of a complex interplay of hormones, and after several days one or occasionally two become dominant (non-dominant follicles atrophy and die). Approximately mid-cycle, 24–36 hours after the Luteinizing Hormone (LH) surges, the dominant follicle releases an ovum, or egg in an event called ovulation. After ovulation, the egg only lives for 24 hours or less without fertilization while the remains of the dominant follicle in the ovary become a corpus luteum; this body has a primary function of producing large amounts of progesterone. Under the influence of progesterone, the endometrium (uterine lining) changes to prepare for potential implantation of an embryo to establish a pregnancy. If implantation does not occur within approximately two weeks, the corpus luteum will involute, causing sharp drops in levels of both progesterone and estrogen. These hormone drops cause the uterus to shed its lining and egg in a process termed menstruation.

In the menstrual cycle, changes occur in the female reproductive system as well as other systems (which lead to breast tenderness or mood changes, for example). A woman's first menstruation is termed menarche, and occurs typically around age 12. The end of a woman's reproductive phase is called the menopause, which commonly occurs somewhere between the ages of 45 and 55.



Primipara = a woman who has delivered one baby.
Multipara = a woman who has delivered two or more babies.
Primip / Primigravida: A woman pregnant for the first time.


The egg cell is released by one of the ovaries and than sucked into a fallopian tube. The lining on the inside of the fallopian tube is also a highly specialized mucus membrane. The cells on the surface of this mucus membrane contain specialized hair like protrusions which is constantly moving in such a way that there is a constant movement of fluid from the ovary towards the opening of tubes and from there toward the cavity in the womb. This movement causes a suction effect. Anything in the vicinity of the ovaries ( like the egg cell) will be sucked into the womb.

An interesting fact is that fertilization does not occur in the womb , but at the opening of the tube near the ovary. The sperms swim all the way from the vagina, through the womb and upstream through the fallopian tubes.

After fertilization the fertilized egg cell is slowly sucked through the fallopian tubes into the cavity of the womb. It only arrives in the womb about five days after conception. The egg than attaches itself to the endometrium ( the lining on the inside of the womb.).

Naegele's Rule is a standard way of calculating the due date for a pregnancy. The rule estimates the expected date of delivery (EDD) by adding one year, subtracting three months, and adding seven days to the first day of a woman's last menstrual period (LMP). The result is approximately 280 days (40 weeks) from the LMP. Naegele's Rule is named after Franz Karl Naegele (1778–1851).

LMP = 8 May 2009
+1 year = 8 May 2010
-3 months = 8 February 2010
+7 days = 15 February 2010



In humans preterm birth refers to the birth of a baby of less than 37 weeks gestational age. The cause for preterm birth is in many situations elusive and unknown; many factors appear to be associated with the development of preterm birth, making the reduction of preterm birth a challenging proposition.

Premature birth, commonly used as a synonym for preterm birth, refers to the birth of a baby before the developing organs are mature enough to allow normal postnatal survival. Premature infants are at greater risk for short and long term complications, including disabilities and impediments in growth and mental development. Significant progress has been made in the care of premature infants, but not in reducing the prevalence of preterm birth. Preterm birth is the major cause of neonatal mortality in developed countries.

Symptoms of imminent spontaneous preterm birth are signs of premature labor; one sign is four or more uterine contractions in one hour. In contrast to false labor, true labor is accompanied by cervical dilatation and effacement. Also, vaginal bleeding in the third trimester, heavy pressure in the pelvis, or abdominal or back pain could be indicators that a preterm birth is about to occur. A watery discharge from the vagina may indicate premature rupture of the membranes that surround the baby. While the rupture of the membranes may not be followed by labor, usually delivery is indicated as infection (chorioamnionitis) is a serious threat to both fetus and mother. In some cases the cervix dilates prematurely without pain or perceived contractions, so that the mother may not have warning signs until very late in the birthing process.

The shorter the term of pregnancy, the greater the risks of mortality and morbidity for the baby primarily due to the related prematurity. Preterm-premature babies ("preemies" or "premmies") have an increased risk of death in the first year of life (infant mortality), with most of that occurring in the first month of life (neonatal mortality). As risk of brain damage and developmental delay is significant at that threshold even if the infant survives.

Preterm infants usually show physical signs of prematurity in reverse proportion to the gestational age. As a result they are at risk for numerous medical problems affecting different organ systems.
Neurological problems include apnea of prematurity, hypoxic-ischemic encephalopathy (HIE), retinopathy of prematurity (ROP), developmental disability, cerebral palsy and intraventricular hemorrhage, the latter affecting 25 percent of babies born preterm, usually before 32 weeks of pregnancy. Mild brain bleeds usually leave no or few lasting complications, but severe bleeds often result in brain damage or even death. Neurodevelopmental problems have been linked to lack of maternal thyroid hormones, at a time when their own thyroid is unable to meet postnatal needs.
 Cardiovascular complications may arise from the failure of the ductus arteriosus to close after birth: patent ductus arteriosus (PDA).
 Respiratory problems are common, specifically the respiratory distress syndrome (RDS or IRDS) (previously called hyaline membrane disease). Another problem can be chronic lung disease (previously called bronchopulmonary dysplasia or BPD).
 Gastrointestinal and metabolic issues can arise from hypoglycemia, feeding difficulties, rickets of prematurity, hypocalcemia, inguinal hernia, and necrotizing enterocolitis (NEC).
 Hematologic complications include anemia of prematurity, thrombocytopenia, and hyperbilirubinemia (jaundice) that can lead to kernicterus.
 Infection, including sepsis, pneumonia, and urinary tract infection.

As the cause of labor still remains elusive, the exact cause of preterm birth is also unsolved. In fact, the cause of 50% of preterm births is never determined. Labor is a complex process involving many factors. Four different pathways have been identified that can result in preterm birth and have considerable evidence: precocious fetal endocrine activation, uterine over-distension, decidual bleeding, and intrauterine inflammation/infection.


 Age at the upper and lower end of the reproductive years, be it more than 35 or less than 18 years of age.
 Maternal height and weight can also play a role.
 Pregnancy interval makes a difference as women with a 6 months span or less between pregnancies have a two-fold increase in preterm birth.
 Studies on type of work and physical activity have given conflicting results, but it is opined that stressful conditions, hard labor, and long hours are probably linked to preterm birth.
 Women who have undergone previous surgically induced abortions have been shown to have a higher risk of preterm birth (less than 37 weeks), as well as extreme preterm birth (less than 28 weeks).
 Adequate maternal nutrition is important. Women with a low BMI are at increased risk for preterm birth. Further, women with poor nutritional status may also be deficient in vitamins and minerals. Adequate nutrition is critical for fetal development and a diet low in saturated fat and cholesterol may help reduce the risk of a preterm delivery. Obesity does not directly lead to preterm birth; however, it is associated with diabetes and hypertension which are risk factors by themselves.
 Women with a previous preterm birth are at higher risk for a recurrence at a rate of 15–50%
 To some degree those individuals may have underlying conditions (i.e. uterine malformation, hypertension, diabetes) that persist.
 Genetic make-up is a factor in the causality of preterm birth.
 Multiple pregnancies (twins, triplets, etc.) are a significant factor in preterm birth.
 Maternal medical conditions increase the risk of preterm birth, and often labor has to be induced for medical reasons; such conditions include high blood pressure, pre-eclampsia, maternal diabetes, asthma, thyroid disease, and heart disease.
   Women with vaginal bleeding during pregnancy are at higher risk for preterm birth.
 Women with abnormal amounts of amniotic fluid, too much (polyhydramnios) or too little (oligohydramnios) are also at risk.
 Babies with birth defects are at higher risk of being born preterm.
 Finally, the use of tobacco, cocaine, and excessive alcohol during pregnancy also increases the chance of preterm delivery.

Historically efforts have been primarily aimed to improve survival and health of preterm infants (tertiary intervention). Such efforts, however, have not reduced the incidence of preterm birth. Increasingly primary interventions that are directed at all women, and secondary intervention that reduce existing risks are looked upon as measures that need to be developed and implemented to prevent the health problems of premature infants and children.



Postmaturity is when a baby has not yet been born after 42 weeks of gestation, two weeks beyond the normal 40. Post-term, postmaturity, prolonged pregnancy, and post-dates pregnancy all refer to postmature birth. Post-mature births do not have any harmful effects on the mother, but the fetus, however, can begin to suffer from malnutrition. After the 42nd week of gestation, the placenta, which supplies the baby with nutrients and oxygen from the mother, starts aging and will eventually fail. If the fetus passes fecal matter, which is not typical until after birth, and the child breathes it in, then the baby could become sick with pneumonia. Postterm pregnancy may be a reason to induce labor.

The causes of post-term births is unknown. But post-mature births are more likely when the mother has experienced a previous post-mature birth. Post-mature births can also be attributed to irregular menstrual cycles. When the menstrual period is irregular it is very difficult to judge how and when the ovaries would be available for fertilization and subsequently result in pregnancy. Some post-mature pregnancies are because the mother is not certain of her last period, so in reality the baby is not technically post-mature.

Different babies will show different symptoms of postmaturity. The most commons symptoms are dry skin, overgrown nails, creases on the baby's palms and soles of their feet, minimal fat, a lot of hair on their head, and either a brown, green, or yellow discoloration of their skin. Doctors diagnose post-mature birth based on the baby's physical appearance and the length of the mother's pregnancy. Some postmature babies will show no or little sign of postmaturity.
Once a pregnancy has surpassed the 40 week gestation period, doctors closely monitor the mother for signs of placental deterioration. Towards the end of pregnancy calcium is deposited on the walls of blood vessels and proteins are deposited on the surface of the placenta, which changes the placenta. This limits the blood flow through the placenta and ultimately leads to placental insufficiency and the baby is no longer properly nourished. Induced labor is strongly encouraged if this happens.
Post-term babies may be larger than an average baby, thus increasing the length of labor. The labor is increased because the baby's head is too big to pass through the mother's pelvis. This is called cephalopelvic disproportion. Caesarean sections are encouraged if this happens.



Gestation is the carrying of an embryo or fetus inside a female viviparous animal. Mammals during pregnancy can have one or more gestations at the same time (multiple gestations). The time interval of a gestation plus two weeks is called gestation period, and the length of time plus two weeks that the offspring have spent developing in the uterus is called gestational age.

Human pregnancy can be divided into three trimesters, each three months long. The first trimester is from the last period to the 13th week, the second trimester is from the 14th to 27th week, and the third trimester is from the 28th week through the 40th week.

In humans, birth normally occurs at a gestational age of about 40 weeks (nine months and one week), though a normal range is from 37 to 42 weeks.


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