Normal Pregnancy

The first lecture that I presented at McMaster University I gave the title “What is normal?” This was about research and laboratory data. A paper had been published by an English university which I disagreed with. The paper was on infertility in patients with “normal Prolactin levels”. In this study the patients had blood samples taken on one occasion in a morning. Prolactin has a diurnal variation (the level changes from morning to night). We had demonstrated marked variations in the same patient at different times of the day, with levels up to five times higher in the evening. The laboratory reports a level against a normal value. However it is never stated if this is an internationally recognised normal, normal for the equipment used, normal for the assay established by that laboratory or normal for that patient. All laboratories have reference levels for healthy men and women but although it is known that levels for most routine laboratory tests change during pregnancy, many laboratories do not show ranges for pregnant women.
There is no such thing as a normal pregnancy – every mother and baby is unique. There are however some common features.
Symptoms of pregnancy
A missed period is usually the first signal of pregnancy, although women with irregular periods may not recognize this. During this time, many women experience a need to urinate frequently, extreme fatigue, nausea and/or vomiting, and increased breast tenderness. Most over-the-counter pregnancy tests are sensitive 9-12 days after conception. During early pregnancy, most women experience an increased appetite.
Weight gain during pregnancy
Weight gain during pregnancy consists of the products of conception (fetus, placenta, amniotic fluid) increase of maternal organs and tissues (uterus, breasts, blood, extracellular fluid, maternal fat stores). The rate of weight gain varies with the trimester. Although weight should be gained throughout pregnancy, it is most critical in the second trimester. The appropriate gestational weight gain depends upon the pre-pregnancy Body Mass Index (BMI). The Institute of Medicine’s 2009 pregnancy weight gain recommendation guidelines for singleton pregnancies are
Underweight (BMI less than 18.5) – 28-40 lbs
Normal weight (BMI of 18.5-24.9) – 25-35 lbs
Overweight (BMI of 25-29.9) – 15-25 lbs
Obese (BMI that exceeds 30) – 11-20 lbs
Women with a low BMI need to gain more weight to produce babies with birth weights comparable to women with a normal BMI. Women with a high BMI can deliver babies with higher birthweights with lower gestational weight gain.
Fetal movement
Most women start to feel fetal movement by 18 to 20 weeks gestation in a first pregnancy, in following pregnancies it can occur as early as 15-16 weeks’ gestation. Early fetal movement is felt most commonly when the woman is sitting or lying quietly. The time at which a woman first feels the baby move is termed quickening.
Breast changes during pregnancy
Pregnancy-related breast changes include growth and enlargement, tenderness, darkening of the nipples, and darkened veins due to increased blood flow. In addition, small raised bumps (Montgomery tubercles) appear around the areola in mid-pregnancy. Colostrum is a yellowish fluid secreted by the breast that can be expressed as early as the 16th week of pregnancy. It is replaced by milk on the second postpartum day.
Skin changes during pregnancy
Pigmentation changes are directly related to melanocyte-stimulating hormone (MSH) elevations during pregnancy. Increased pigmentation of some form affects 90% of pregnant women but is more obvious in women with darker skin. This is typically evident in the nipples, umbilicus, axillae and perineum, the linea alba darkens to a brown line called the linea nigra on the midline of the abdomen. Pre-existing moles, freckles and recent scars also become darker. Melasma (also known as chloasma or the mask of pregnancy) is a tan or dark skin discoloration. These are seen in 75% of pregnant women and are commonly found on the upper cheek, nose, lips and forehead. Most of these changes regress after delivery but may recur in future pregnancies.
Striae gravidarum (stretch marks) occur in most pregnant women, usually by the end of the second trimester. In Caucasian women the incidence is reported as 90%. Stretch marks usually occur when weight is lost or gained quickly and the degree to which a woman experiences stretch marks is determined genetically. They usually fade and pale with time.
Hair changes in pregnancy are very common both scalp and body hair. Hirsutism (excessive growth of body hair) is seen in many pregnant women. Thickening of scalp hair during pregnancy is usually followed by increased hair shedding one to four months after delivery.
Sebaceous gland activity is increased during the second half of pregnancy causing greasy skin and possibly acne.
Haemorrhoids and varicose veins
As pregnancy progresses the combination of increased blood volume, circulating progesterone effect on blood vessels and pressure of the growing uterus result in haemorrhoids being more common during pregnancy.
Varicose veins may also appear for the first time during pregnancy due to the relaxant effect of progesterone on blood vessel walls and stasis in leg vessels caused by pressure of the uterus.
Labour
The onset of labour is regular contractions resulting in progressive cervical changes. A “show” (blood stained mucus discharge) or spontaneous rupture of the membranes (waters breaking) do not of themselves define the onset of labour. Despite the prevalence of “waters breaking” heralding the start of labour in films and TV dramas, this occurs before regular contractions in less than 8% of pregnancies.
The duration of labour varies with different populations and management practices. A general guideline would be that in most first pregnancies labour lasts less than 12 hours and this is reduced to less than 8 hours in subsequent pregnancies.
Most blood loss related to childbirth occurs within the first hour after birth. In vaginal deliveries up to 500ml of blood may be lost from the genital tract within 24 hours after birth, some of which may appear as clots.