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

Locked twins is a rare complication of multiple pregnancy where two fetuses become interlocked during presentation before birth. It occurs in roughly 1 in 1,000 twin deliveries and 1 in 90,000 deliveries overall. Most often, locked twins are delivered via Caesarean section, given that the condition has been diagnosed early enough. The fetal mortality rate is high for the twin that presents first, with over 50% being stillborn.

A vanishing twin, also known as fetal resorption, is a fetus in a multi-gestation pregnancy which dies in utero and is then partially or completely reabsorbed. In some instances, the dead twin will be compressed into a flattened, parchment-like state known as "fetus papyraceus".

Vanishing twins occur in up to one out of every eight multifetus pregnancies and may not even be known in most cases. "High resorption rates, which cannot be explained on the basis of the expected abortion rate...suggest intense fetal competition for space, nutrition, or other factors during early gestation, with frequent loss or resorption of the other twin(s)."

In pregnancies achieved by IVF, "it frequently happens that more than one amniotic sac can be seen in early pregnancy, whereas a few weeks later there is only one to be seen and the other has 'vanished'."

The common clinical features are smaller symphysis fundal height, fetal malpresentation, undue prominence of fetal parts and reduced amount of amniotic fluid.

In medicine (obstetrics), the term fetal distress refers to the presence of signs in a pregnant woman—before or during childbirth—that suggest that the fetus may not be well. Because of its lack of precision, the term is eschewed in modern American obstetrics.

Generally it is preferable to describe specific signs in lieu of declaring "fetal distress" that include:

- Decreased movement felt by the mother

- Meconium in the amniotic fluid ("meconium stained fluid")

- Non-reassuring patterns seen on cardiotocography:

- increased or decreased fetal heart rate (tachycardia and bradycardia), especially during and after a contraction

- decreased variability in the fetal heart rate

- late decelerations

- Biochemical signs, assessed by collecting a small sample of baby's blood from a scalp prick through the open cervix in labor

- fetal metabolic acidosis

- elevated fetal blood lactate levels (from fetal scalp blood testing) indicating the baby has a lactic acidosis

Some of these signs are more reliable predictors of fetal compromise than others. For example, cardiotocography can give high false positive rates, even when interpreted by highly experienced medical personnel. Metabolic acidosis is a more reliable predictor, but is not always available.

Factors that predispose to face presentation are prematurity, macrosomia, anencephaly and other malformations, cephalopelvic disproportion, and polyhydramnios. In an uncomplicated face presentation duration of labor is not altered. Perinatal losses with face presentation occur with traumatic version and extraction and midforceps procedures Duff indicates that the prevalence of face presentations is about 1/500–600., while Benedetti et al. found it to be 1/1,250 term deliveries.

Face presentations are classified according to the position of the chin (mentum):

- Left Mento-Anterior (LMA), Left Mento-Posterior (LMP), Left Mento-Transverse (LMT);

- Right Mento-Anterior (RMA), Right Mento-Posterior (RMP), Right Mento-Transverse (RMT);

The Oskie presentation is similar to the Occipito-Anterior position where the baby is head down, facing the spine, with back on the ventral side of the uterus; however, in this position while the torso is aligned with the mother's longitudinal axis the legs of the fetus are extended straight along the frontal axis of the mother, as if the baby is creating a right angle with his body. For the Oskie position to occur the baby's head must be far down the pelvis in order to allow room for leg extension, typically the arms are bent, tucked against the baby's body. There are no known complications for labor and delivery. This presentation is rare and is not well researched.

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

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.

There are two types of locked twins: breech/vertex and vertex/vertex. In breech/vertex presentations, which are much more common, the first twin is in the breech position, presenting feet-first, and the second is in the cephalic (vertex) position, presenting in the normal head-first manner. In these cases, the chin of the first twin locks behind the chin of the second twin while in the uterus or birth canal, preventing vaginal delivery. In vertex/vertex presentations, where both twins are positioned for head-first delivery, the two heads become locked at the pelvic brim, preventing either fetus from passing through the pelvic inlet in a vaginal delivery.

Contributing factors to the interlocking of twins include uterine hypertonicity, small fetal size, and reduced levels of amniotic fluid following rupture of the membranes. It is more likely to occur in women with large pelvises, young primigravidae (young women in their first pregnancy), and pregnancies with monoamniotic twins.

Complications may include cord compression, musculoskeletal abnormalities such as facial distortion and clubfoot, pulmonary hypoplasia and intrauterine growth restriction. Amnion nodosum is frequently also present (nodules on the fetal surface of the amnion).

The use of oligohydramnios as a predictor of gestational complications is controversial.

Potter syndrome is a condition caused by oligohydramnios. Affected fetuses develop pulmonary hypoplasia, limb deformities, and characteristic facies. Bilateral agenesis of the fetal kidneys is the most common cause due to the lack of fetal urine.

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).

The symptoms and discomforts of pregnancy are those presentations and conditions that result from pregnancy but do not significantly interfere with activities of daily living or pose a threat to the health of the mother or baby. This is in contrast to pregnancy complications. Sometimes a symptom that is considered a discomfort can be considered a complication when it is more severe. For example, nausea (morning sickness) can be a discomfort, but if, in combination with significant vomiting it causes a water-electrolyte imbalance, it is a complication known as hyperemesis gravidarum.

Common symptoms and discomforts of pregnancy include:

- Tiredness.

- Constipation

- Pelvic girdle pain

- Back pain

- Braxton Hicks contractions. Occasional, irregular, and often painless contractions that occur several times per day.

- Edema (swelling). 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.

- Increased urinary frequency. 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.

- Haemorrhoids (piles). 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.

- Regurgitation, heartburn, and nausea.

- Stretch marks

- Breast tenderness is common during the first trimester, and is more common in women who are pregnant at a young age.

In addition, pregnancy may result in pregnancy complication such as deep vein thrombosis or worsening of an intercurrent disease in pregnancy.

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

Women with placenta previa often present with painless, bright red vaginal bleeding. This commonly occurs around 32 weeks of gestation, but can be as early as late mid-trimester. 51.6% of women with placenta previa have antepartum haemorrhage. This bleeding often starts mildly and may increase as the area of placental separation increases. Previa should be suspected if there is bleeding after 24 weeks of gestation. Bleeding after delivery occurs in about 22% of those affected.

Women may also present as a case of failure of engagement of fetal head.

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.

Fetus in fetu (or foetus in foetu) is a developmental abnormality in which a mass of tissue resembling a fetus forms inside the body. An early example of the phenomenon was described in 1808 by George William Young.

There are two theories of origin concerning "fetus in fetu". One theory is that the mass begins as a normal fetus but becomes enveloped inside its twin. The other theory is that the mass is a highly developed teratoma. "Fetus in fetu" is estimated to occur in 1 in 500,000 live births.

An abdominal pregnancy can be regarded as a form of an ectopic pregnancy where the embryo or fetus is growing and developing outside the womb in the abdomen, but not in the Fallopian tube, ovary or broad ligament.

While rare, abdominal pregnancies have a higher chance of maternal mortality, perinatal mortality and morbidity compared to normal and ectopic pregnancies; on occasion, however, a healthy viable infant can be delivered.

Because tubal, ovarian and broad ligament pregnancies are as difficult to diagnose and treat as abdominal pregnancies, their exclusion from the most common definition of abdominal pregnancy has been debated.

Others—in the minority—are of the view that abdominal pregnancy should be defined by a placenta implanted into the peritoneum.

Placental abruption is when the placenta separates early from the uterus, in other words separates before childbirth. It occurs most commonly around 25 weeks of pregnancy. Symptoms may include vaginal bleeding, lower abdominal pain, and dangerously low blood pressure. Complications for the mother can include disseminated intravascular coagulopathy and kidney failure. Complications for the baby can include fetal distress, low birthweight, preterm delivery, and stillbirth.

The cause of placental abruption is not entirely clear. Risk factors include smoking, preeclampsia, prior abruption, trauma during pregnancy, cocaine use, and previous cesarean section. Diagnosis is based on symptoms and supported by ultrasound. It is classified as a complication of pregnancy.

For small abruption bed rest may be recommended while for more significant abruptions or those that occur near term, delivery may be recommended. If everything is stable vaginal delivery may be tried, otherwise cesarean section is recommended. In those less than 36 weeks pregnant, corticosteroids may be given to speed development of the babies lungs. Treatment may require blood transfusion or emergency hysterectomy.

Placental abruption occurs in about 1 in 200 pregnancies. Along with placenta previa and uterine rupture it is one of the most common cause of vaginal bleeding in the later part of pregnancy. Placental abruption is the reason for about 15% of infant deaths around the time of birth. The condition was described at least as early as 1664.

Symptoms may include abdominal pain or vaginal bleeding during pregnancy. As this is nonspecific in areas where ultrasound is not available the diagnosis was often only discovered during surgery to investigate the abnormal symptoms. They are typically diagnosed later in the developing world than the developed. In about half of cases from a center in the developing world the diagnosis was initially missed.

It is a dangerous condition as there can be bleeding into the abdomen that results in low blood pressure and can be fatal. Other causes of death in people with an abdominal pregnancy include anemia, pulmonary embolus, coagulopathy, and infection.

Placenta praevia is when the placenta attaches inside the uterus but near or over the cervical opening. Symptoms include vaginal bleeding in the second half of pregnancy. The bleeding is bright red and tends not to be associated with pain. Complications may include placenta accreta, dangerously low blood pressure, or bleeding after delivery. Complications for the baby may include fetal growth restriction.

Risk factors include pregnancy at an older age and smoking as well as prior cesarean section, labor induction, or termination of pregnancy. Diagnosis is by ultrasound. It is classified as a complication of pregnancy.

For those who are less than 36 weeks pregnant with only a small amount of bleeding recommendations may include bed rest and avoiding sexual intercourse. For those after 36 weeks of pregnancy or with a significant amount of bleeding, cesarean section is generally recommended. In those less than 36 weeks pregnant, corticosteroids may be given to speed development of the babies lungs. Cases that occur in early pregnancy may resolve on their own.

It affects approximately 0.5% of pregnancies. After four cesarean section it, however, effects 10% of pregnancies. Rates of disease have increased over the late 20th century and early 21st century. The condition was first described in 1685 by Paul Portal.

Premature rupture of membranes (PROM), or pre-labor rupture of membranes, is a condition that can occur in pregnancy. It is defined as rupture of membranes (breakage of the amniotic sac), commonly called breaking of the mother's water(s), more than 1 hour before the onset of labor. The sac (consisting of 2 membranes, the chorion and amnion) contains amniotic fluid, which surrounds and protects the fetus in the uterus (womb). After rupture, the amniotic fluid leaks out of the uterus, through the vagina.

Women with PROM usually experience a painless gush of fluid leaking out from the vagina, but sometimes a slow steady leakage occurs instead.

When premature rupture of membranes occurs at or after 37 weeks completed gestational age (full-term or term), there is minimal risk to the fetus and labor typically starts soon after.

If rupture occurs before 37 weeks, it is called preterm premature rupture of membranes (PPROM), and the fetus and mother are at greater risk for complications. PPROM causes one-third of all preterm births, and babies born preterm (before 37 weeks) can suffer from the complications of prematurity, including death.

Premature rupture of the membranes provides a path for bacteria to enter the womb and puts both the mother and fetus at risk for life-threatening infection. Low levels of fluid around the fetus also increase the risk of umbilical cord compression and can interfere with lung and body formation in early pregnancy.

Women who suspect they might have experienced premature rupture of membranes should be evaluated promptly in the hospital to determine whether a rupture of membranes has indeed occurred, and to be treated appropriately to avoid infection and other complications.

A large fetus can be one case of CPD. A large fetus can be caused by gestational diabetes, postterm pregnancy, genetic factors, and multiparity.

The shape of the pelvis can also be a cause of CPD. The pelvis may be too small, or the shape of the pelvis may be malformed. Shorter women are more likely to suffer from CPD as are adolescents.

Cephalo-pelvic disproportion exists when the capacity of the pelvis is inadequate to allow the fetus to negotiate the birth canal. This may be due to a small pelvis, a nongynecoid pelvic formation, a large fetus, an unfavorable orientation of the fetus, or a combination of these factors. Certain medical conditions may distort pelvic bones, such as rickets or a pelvic fracture, and lead to CPD.

Transverse diagonal measurement has been proposed as a predictive method.