There are 2 major categories of IUGR: symmetrical and asymmetrical. Some conditions are associated with both symmetrical and asymmetrical growth restriction.

Asymmetrical IUGR is more common (70%). In asymmetrical IUGR, there is restriction of weight followed by length. The head continues to grow at normal or near-normal rates (head sparing). A lack of subcutaneous fat leads to a thin and small body out of proportion with the liver. Normally at birth the brain of the fetus is 3 times the weight of its liver. In IUGR, It becomes 5-6 times. In these cases, the embryo/fetus has grown normally for the first two trimesters but encounters difficulties in the third, sometimes secondary to complications such as pre-eclampsia. Other symptoms than the disproportion include dry, peeling skin and an overly-thin umbilical cord. The baby is at increased risk of hypoxia and hypoglycaemia. This type of IUGR is most commonly caused by extrinsic factors that affect the fetus at later gestational ages. Specific causes include:

- Chronic high blood pressure

- Severe malnutrition

- Genetic mutations, Ehlers–Danlos syndrome

Being small for gestational age is broadly either:

- Being constitutionally small, wherein the state is basically a genetic trait of the baby.

- Intrauterine growth restriction, also called "pathological SGA"

Small for gestational age (SGA) newborns are those who are smaller in size than normal for the gestational age, most commonly defined as a weight below the 10th percentile for the gestational age.

Having one or more parents in the 90th percentile for size is likely to lead to a false positive concern for LGA.

One of the primary risk factors of LGA is poorly-controlled diabetes, particularly gestational diabetes (GD), as well as preexisting diabetes mellitus (DM) (preexisting type 2 is associated more with macrosomia, while preexisting type 1 can be associated with microsomia). This increases maternal plasma glucose levels as well as insulin, stimulating fetal growth. The LGA newborn exposed to maternal DM usually only has an increase in weight. LGA newborns that have complications other than exposure to maternal DM present with universal measurements above the 90th percentile.

LGA and macrosomia cannot be diagnosed until after birth, as it is impossible to accurately estimate the size and weight of a child in the womb. Babies that are large for gestational age throughout the pregnancy may be suspected because of an ultrasound, but fetal weight estimations in pregnancy are quite imprecise. For non-diabetic women, ultrasounds and care providers are equally inaccurate at predicting whether or not a baby will be big. If an ultrasound or a care provider predicts a big baby, they will be wrong half the time.

Although big babies are born to only 1 out of 10 women, the 2013 Listening to Mothers Survey found that 1 out of 3 American women were told that their babies were too big. In the end, the average birth weight of these suspected “big babies” was only . In the end, care provider concerns about a suspected big baby were the fourth-most common reason for an induction (16% of all inductions), and the fifth-most common reason for a C-section (9% of all C-sections). This treatment is not based on current best evidence.

Research has consistently shown that, as far as birth complications are concerned, the care provider’s perception that a baby is big is more harmful than an actual big baby by itself. In a 2008 study, researchers compared what happened to women who were suspected of having a big baby to what happened to women who were not suspected of having a big baby—but who ended up having one. In the end, women who were suspected of having a big baby (and actually had one) had a triple in the induction rate, more than triple the C-section rate, and a quadrupling of the maternal complication rate, compared to women who were not suspected of having a big baby but who had one anyway.

Complications were most often due to C-sections and included bleeding (hemorrhage), wound infection, wound separation, fever, and need for antibiotics. There were no differences in shoulder dystocia between the two groups. In other words, when a care provider “suspected” a big baby (as compared to not knowing the baby was going to be big), this tripled the C-section rates and made mothers more likely to experience complications, without improving the health of babies.

Low birth weight (LBW) is defined by the World Health Organization as a birth weight of a

infant of 2,499 g or less, regardless of gestational age. Subcategories include very low birth weight (VLBW), which is less than 1500 g (3 pounds 5 ounces), and extremely low birth weight (ELBW), which is less than 1000 g (2 pounds 3 ounces). Normal weight at term delivery is 2500–4200 g (5 pounds 8 ounces – 9 pounds 4 ounces).

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, transient hyperammonemia of the newborn, 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 neonatal 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

A study of 241 children born between 22 and 25 weeks who were currently of school age found that 46 percent had severe or moderate disabilities such as cerebral palsy, vision or hearing loss and learning problems. 34 percent were mildly disabled and 20 percent had no disabilities, while 12 percent had disabling cerebral palsy.

LBW is either caused by preterm birth (that is, a low gestational age at birth, commonly defined as younger than 37 weeks of gestation) or the infant being small for gestational age (that is, a slow prenatal growth rate), or a combination of both.

In general, risk factors in the mother that may contribute to low birth weight include young ages, multiple pregnancies, previous LBW infants, poor nutrition, heart disease or hypertension, untreated coeliac disease, drug addiction, alcohol abuse, and insufficient prenatal care. Environmental risk factors include smoking, lead exposure, and other types of air pollutions.

Preterm birth causes a range of problems.

The main categories of causes of preterm birth are preterm labor induction and spontaneous preterm labor. Signs and symptoms of preterm labor include four or more uterine contractions in one hour. In contrast to false labour, 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.

A review into using uterine monitoring at home to detect contractions and possible preterm births in women at higher risk of having a preterm baby found that it did not reduce the number of preterm births. The research included in the review was poor quality but it showed that home monitoring may increase the number of unplanned antenatal visits and may reduce the number of babies admitted to special care when compared with women receiving normal antenatal care.

Hyperemesis gravidarum is the presence of severe and persistent vomiting, causing dehydration and weight loss. It is more severe than the more common morning sickness and is estimated to affect 0.5–2.0% of pregnant women.

Gestational diabetes is when a woman without diabetes develops high blood sugar levels during pregnancy.

No single diagnostic test currently exists to predict the likelihood of developing gestational hypertension. High blood pressure is the major sign in diagnosing gestational hypertension. Protein in the urine, proteinuria, is a key indicator of the condition. Some women with gestational hypertension may present asymptomatic, but a number of symptoms are associated with the condition.

Symptoms

- Edema

- Sudden weight gain

- Blurred vision or sensitivity to light

- Nausea and vomiting

- Persistent headaches

- Increased blood pressure

Each year, ill health as a result of pregnancy is experienced (sometimes permanently) by more than 20 million women around the world. In 2013 complications of pregnancy resulted in 293,000 deaths down from 377,000 deaths in 1990. Common causes include maternal bleeding (44,000), complications of abortion (44,000), high blood pressure of pregnancy (29,000), maternal sepsis (24,000), and obstructed labor (19,000).

The following are some examples of pregnancy complications:

- Pregnancy induced hypertension

- Anemia

- Postpartum depression

- Postpartum psychosis

- Thromboembolic disorders. These are the leading cause of death in pregnant women in the US.

- PUPPP (Pruritic Urticarial Papules and Plaques of Pregnancy), a skin disease that develops around the 32nd week. Signs are red plaques, papules, and itchiness around the belly button that then spreads all over the body except for the inside of hands and face.

- Ectopic pregnancy, implantation of the embryo outside the uterus.

- Hyperemesis gravidarum, excessive nausea and vomiting that is more severe than normal morning sickness.

- Pulmonary embolism, blood clots that form in the legs that can migrate to the lungs.

There is also an increased susceptibility and severity of certain infections in pregnancy.

Placental villous immaturity, also villous immaturity and villous dysmaturity, is chorionic villous development that is inappropriate for the gestational age.

It is associated with diabetes mellitus

and fetal death near term, i.e. intrauterine demise close to the normal gestational period.

Unfortunately, there is no single test to predict or diagnose preeclampsia. Key signs are increased blood pressure and protein in the urine (proteinuria). Other symptoms that seem to occur with preeclampsia include persistent headaches, blurred vision or sensitivity to light, and abdominal pain.

All of these sensations can be caused by other disorders; they can also occur in healthy pregnancies. Regular visits are scheduled to track blood pressure and level of protein in urine, to order and analyze blood tests that detect signs of preeclampsia, and to monitor fetal development more closely.

The beginning of pregnancy may be detected either based on symptoms by the woman herself, or by using pregnancy tests. However, an important condition with serious health implications that is quite common is the denial of pregnancy by the pregnant woman. About one in 475 denials will last until around the 20th week of pregnancy. The proportion of cases of denial, persisting until delivery is about 1 in 2500. Conversely, some non-pregnant women have a very strong belief that they are pregnant along with some of the physical changes. This condition is known as a false pregnancy.

In the early stages of placental abruption, there may be no symptoms. When symptoms develop, they tend to develop suddenly. Common symptoms include sudden-onset abdominal pain, contractions that seem continuous and do not stop, vaginal bleeding, enlarged uterus disproportionate to the gestational age of the fetus, decreased fetal movement, and decreased fetal heart rate.

Vaginal bleeding, if it occurs, may be bright red or dark.

A placental abruption caused by arterial bleeding at the center of the placenta leads to sudden development of severe symptoms and life-threatening conditions including fetal heart rate abnormalities, severe maternal hemorrhage, and disseminated intravascular coagulation (DIC). Those abruptions caused by venous bleeding at the periphery of the placenta develop more slowly and cause small amounts of bleeding, intrauterine growth restriction, and oligohydramnios (low levels of amniotic fluid).

A classification of hypertensive disorders of pregnancy uses 4 categories:

1. chronic hypertension;

2. preeclampsia-eclampsia;

3. preeclampsia superimposed on chronic hypertension;

4. gestational hypertension (transient hypertension of pregnancy or chronic hypertension identified in the latter half of pregnancy).

This terminology is preferred over the older but widely used term pregnancy-induced hypertension (PIH) because it is more precise. The newer terminology reflects simply relation of pregnancy with either the onset or first detection of hypertension and that the question of causation, while pathogenetically interesting, is not the important point for most health care purposes. This classification treats HELLP syndrome as a type of preeclampsia rather than a parallel entity.

Gestational hypertension or pregnancy-induced hypertension (PIH) is the development of new hypertension in a pregnant woman after 20 weeks gestation without the presence of protein in the urine or other signs of preeclampsia. Hypertension is defined as having a blood pressure

greater than 140/90 mm Hg.

Placental villous immaturity, as the name implies, is characterized by chorionic villi that are inappropriately developed for the gestational age. The development and maturation of chorionic villi is essential for normal fetal development.

Immature chorionic villi are larger and have more central blood vessels; thus, the diffusion distance for gas and nutrient exchange is larger and, therefore, placental function is impaired.

Antepartum bleeding, also known as antepartum haemorrhage or prepartum hemorrhage, is genital bleeding during pregnancy from the 28th week (sometimes defined as from the 20th week) gestational age to term.

It can be associated with reduced fetal birth weight.

In regard to treatment, it should be considered a medical emergency (regardless of whether there is pain) and medical attention should be sought immediately, as if it is left untreated it can lead to death of the mother and/or fetus.

Gestational diabetes is formally defined as "any degree of glucose intolerance with onset or first recognition during pregnancy". This definition acknowledges the possibility that a woman may have previously undiagnosed diabetes mellitus, or may have developed diabetes coincidentally with pregnancy. Whether symptoms subside after pregnancy is also irrelevant to the diagnosis.

A woman is diagnosed with gestational diabetes when glucose intolerance continues beyond 24–28 weeks of gestation.

The White classification, named after Priscilla White, who pioneered research on the effect of diabetes types on perinatal outcome, is widely used to assess maternal and fetal risk. It distinguishes between gestational diabetes (type A) and pregestational diabetes (diabetes that existed prior to pregnancy). These two groups are further subdivided according to their associated risks and management.

The two subtypes of gestational diabetes under this classification system are:

- Type A1: abnormal oral glucose tolerance test (OGTT), but normal blood glucose levels during fasting and two hours after meals; diet modification is sufficient to control glucose levels

- Type A2: abnormal OGTT compounded by abnormal glucose levels during fasting and/or after meals; additional therapy with insulin or other medications is required

Diabetes which existed prior to pregnancy is also split up into several subtypes under this system:

- Type B: onset at age 20 or older and duration of less than 10 years.

- Type C: onset at age 10–19 or duration of 10–19 years.

- Type D: onset before age 10 or duration greater than 20 years.

- Type E: overt diabetes mellitus with calcified pelvic vessels.

- Type F: diabetic nephropathy.

- Type R: proliferative retinopathy.

- Type RF: retinopathy and nephropathy.

- Type H: ischemic heart disease.

- Type T: prior kidney transplant.

An early age of onset or long-standing disease comes with greater risks, hence the first three subtypes.

Two other sets of criteria are available for diagnosis of gestational diabetes, both based on blood-sugar levels.

Criteria for diagnosis of gestational diabetes, using the 100 gram Glucose Tolerance Test, according to Carpenter and Coustan:

- Fasting 95 mg/dl

- 1 hour 180 mg/dl

- 2 hours 155 mg/dl

- 3 hours 140 mg/dl

Criteria for diagnosis of gestational diabetes according to National Diabetes Data Group:

- Fasting 105 mg/dl

- 1 hour 190 mg/dl

- 2 hours 165 mg/dl

- 3 hours 145 mg/dl

For pregnant women with diabetes mellitus some particular challenges for both mother and child. If the woman has diabetes as an intercurrent disease in pregnancy, it can cause early labor, birth defects, and very large babies.

Planning in advance is emphasized if one wants to have a baby and has type 1 diabetes mellitus or type 2 diabetes mellitus. Pregnancy management for diabetics needs stringent blood glucose control even in advance of having pregnancy.

The White classification, named after Priscilla White who pioneered research on the effect of diabetes types on perinatal outcome, is widely used to assess maternal and fetal risk. It distinguishes between gestational diabetes (type A) and diabetes that existed before pregnancy (pregestational diabetes). These two groups are further subdivided according to their associated risks and management.

There are 2 classes of gestational diabetes (diabetes which began during pregnancy):

- Class A: gestational diabetes; diet controlled

- Class A: gestational diabetes; medication controlled

The second group of diabetes which existed before pregnancy can be split up into these classes:

- Class B: onset at age 20 or older or with duration of less than 10 years

- Class C: onset at age 10-19 or duration of 10–19 years

- Class D: onset before age 10 or duration greater than 20 years

- Class E: overt diabetes mellitus with calcified pelvic vessels

- Class F: diabetic nephropathy

- Class R: proliferative retinopathy

- Class RF: retinopathy and nephropathy

- Class H: ischemic heart disease

- Class T: prior kidney transplant

An early age of onset or long-standing disease comes with greater risks, hence the first three subtypes.