In pregnancy, there is an increased susceptibility and/or severity of several infectious diseases.

The signs and symptoms of a vertically transmitted infection depend on the individual pathogen. It may cause subtle signs such as a influenza-like illness and may not even be noticed by the mother during the pregnancy. In such cases, the effects may be seen first at birth.

Symptoms of a vertically transmitted infection may include fever and flu like symptoms. The newborn is often small for gestational age. A petechial rash on the skin may be present, with small reddish or purplish spots due to bleeding from capillaries under the skin. An enlarged liver and spleen (hepatosplenomegaly) is common, as is jaundice. However, jaundice is less common in hepatitis B because a newborn's immune system is not developed well enough to mount a response against liver cells, as would normally be the cause of jaundice in an older child or adult. Hearing impairment, eye problems, mental retardation, autism, and death can be caused by vertically transmitted infections. The mother often has a mild infection with few or no symptoms.

The genetic conditions of Aicardi-Goutieres syndrome are possibly present in a similar manner.

There are several potential risk factors or causes to this increased risk:

- An increased immune tolerance in pregnancy to prevent an immune reaction against the fetus

- Maternal physiological changes including a decrease in respiratory volumes and urinary stasis due to an enlarging uterus.

- The presence of a placenta for pathogens to use as a habitat, such as by "L. monocytogenes" and "P. falciparum".

Neonatal infections are infections of the neonate (newborn) during the neonatal period or first four weeks after birth. Neonatal infections may be contracted by transplacental transfer in utero, in the birth canal during delivery (perinatal), or by other means after birth. Some neonatal infections are apparent soon after delivery, while others may develop postpartum within the first week or month. Some infections acquired in the neonatal period do not become apparent until much later such as HIV, hepatitis B and malaria.

There is a higher risk of infection for preterm or low birth weight neonates. Respiratory tract infections contracted by preterm neonates may continue into childhood or possibly adulthood with long-term effects that limit one's ability to engage in normal physical activities, decreasing one's quality of life and increasing health care costs. In some instances, neonatal respiratory tract infections may increase one's susceptibility to future respiratory infections and inflammatory responses related to lung disease.

Antibiotics can be effective treatments for neonatal infections, especially when the pathogen is quickly identified. Instead of relying solely on culturing techniques, pathogen identification has improved substantially with advancing technology; however, neonate mortality has not kept pace and remains 20% to 50%. While preterm neonates are at a particularly high risk, full term and post-term infants can also develop infection. Neonatal infection may also be associated with premature rupture of membranes (breakage of the amniotic sac) which substantially increases the risk of neonatal sepsis by allowing passage for bacteria to enter the womb prior to the birth of the infant. Neonatal infection can be distressing to the family and it initiates concentrated effort to treat it by clinicians.Research to improve treatment of infections and prophylactic treatment of the mother to avoid infections of the infant is ongoing.

A vertically transmitted infection can be called a perinatal infection if it is transmitted in the perinatal period, which is the period starting at a gestational age of between 22 and 28 weeks (with regional variations in the definition) and ending seven completed days after birth.

The term congenital infection can be used if the vertically transmitted infection persists after childbirth.

Women experiencing PAM may exhibit normal symptoms of malaria, but may also be asymptomatic or present with more mild symptoms, including a lack of the characteristic fever. This may prevent a woman from seeking treatment despite the danger to herself and her unborn child.

Diagnosis of infection is based upon the recovery of the pathogen or pathogens from the typically sterile sites in the mother or the baby. Unfortunately, as many half of pregnant women are asymptomatic with a gonorrhea infection and other sexually transmitted infections. Samples are obtained from urine, blood or cerebrospinal fluid. Diagnosis of infection can also be aided by the use of more nonspecific tests such as determining the total white blood cell count, cytokine levels and other blood tests and signs.

Pregnancy-associated malaria (PAM) or placental malaria is a presentation of the common illness that is particularly life-threatening to both mother and developing fetus. PAM is caused primarily by infection with "Plasmodium falciparum", the most dangerous of the four species of malaria-causing parasites that infect humans. During pregnancy, a woman faces a much higher risk of contracting malaria and of associated complications. Prevention and treatment of malaria are essential components of prenatal care in areas where the parasite is endemic.

While the average adult citizen of an endemic region possesses some immunity to the parasite, pregnancy causes complications that leave the woman and fetus extremely vulnerable. The parasite interferes with transmission of vital substances through the fetal placenta, often resulting in stillbirth, spontaneous abortion, or dangerously low birth weight. The tragedy of malaria in developing countries receives abundant attention from the international health community, but until recently PAM and its unique complications were not adequately addressed.

Congenital cytomegalovirus infection refers to a condition where cytomegalovirus is transmitted in the prenatal period.

Human cytomegalovirus is one of the vertically transmitted infections that lead to congenital abnormalities. (Others are: toxoplasmosis, rubella, and herpes simplex. )

HIV in pregnancy is the presence of the HIV virus in a woman while pregnant. There are concerns because women diagnosed with HIV/AIDS may transmit the infection to their child during pregnancy. The infection be transmitted to the infant during the pregnancy, childbirth, or breastfeeding. However, the risk of mother-to-child transmission of HIV may be reduced by the use of HIV medications known as antiretroviral therapy (ART). These medications may be used by women before, during, and after pregnancy. After delivery, children are also given the medication to reduce the risk of infection. Because HIV may be spread through breast milk, mothers with the infection are encouraged to avoid breastfeeding.

Infection with HIV/AIDS is not a contraindication to pregnancy. Women with the disease may choose to become pregnant if they desire, however, they are encouraged to talk with their doctors beforehand. Some women are unaware they have the disease until they become pregnant. In this case, they should begin antiretroviral therapy as soon as possible. With the appropriate treatment, the risk of mother-to-child infection can be reduced to below 1%. Without treatment, the risk of transmission is 15-45%.

There are approximately 1.4 million HIV positive women who become pregnant and contribute to more than 300,000 neonatal and fetal deaths each year. With the use of ART, transmission of HIV from the mother to child has decreased according to reports by the World Health Organization (WHO). In 2009, there were an estimated 400,000 children born with HIV and by 2013, there were 240,000. Countries in Southern Africa are worst affected by the HIV/AIDS pandemic. In 2010, 30% of all pregnancies in the region were affected by HIV. In 2011, HIV was responsible for 50% of the deaths for children below the age of 5. In the United States, fewer than 200 babies are born with HIV every year.

As of 2015, Cuba has become the first country in the world to eradicate mother-to-child transmission of HIV. In 2010, the WHO partnered with the Pan American Health Organization (PAHO) to implement an initiative that would provide early prenatal care and HIV testing for all pregnant women in the country. For women who tested positive, ART was provided for both the mother and child, cesarean sections were performed, and alternatives to breastfeeding were provided. In implementing these measures, the country was successfully able to eradicate HIV transmission during pregnancy.

For infants who are infected by their mothers before birth, two potential adverse scenarios exist:

- Generalized infection may occur in the infant, and can cause complications such as low birth weight, microcephaly, seizures, petechial rash similar to the "blueberry muffin" rash of congenital rubella syndrome, and moderate hepatosplenomegaly (with jaundice). Though severe cases can be fatal, with supportive treatment most infants with CMV disease will survive. However, from 80% to 90% will have complications within the first few years of life that may include hearing loss, vision impairment, and varying degrees of learning disability.

- Another 5% to 10% of infants who are infected but without symptoms at birth will subsequently have varying degrees of hearing and mental or coordination problems. The onset of hearing loss can occur at any point during childhood, although commonly within the first decade. It is progressive and can affect both ears.

These risks appear to be almost exclusively associated with women who previously have not been infected with CMV and who are having their first infection with the virus during pregnancy. There appears to be little risk of CMV-related complications for women who have been infected at least 6 months prior to conception. For this group, which makes up 50% to 80% of the women of child-bearing age, the rate of newborn CMV infection is 1%, and these infants appear to have no significant illness or abnormalities.

The virus can also be transmitted to the infant at delivery from contact with genital secretions or later in infancy through breast milk. However, these infections usually result in little or no clinical illness in the infant.

To summarise, during a pregnancy when a woman who has never had CMV infection becomes infected with CMV, there is a risk that after birth the infant may have CMV-related complications, the most common of which are associated with hearing loss, visual impairment, or diminished mental and motor capabilities. On the other hand, healthy infants and children who acquire CMV after birth have few, if any, symptoms or complications. However, preterm born infants infected with CMV after birth (especially via breastmilk). This can lead to cognitive and motor impairments later in life.

Congenital cytomegalovirus infection can be an important cause of intraventricular hemorrhage and neonatal encephalopathy.

Chorioamnionitis also known as intra-amniotic infection (IAI) is an inflammation of the fetal membranes (amnion and chorion) due to a bacterial infection. It typically results from bacteria ascending into the uterus from the vagina and is most often associated with prolonged labor. The risk of developing chorioamnionitis increases with each vaginal examination that is performed in the final month of pregnancy, including during labor.

It had also been associated with a number of diseases in humans, including nonspecific urethritis, and infertility.

Chorioamnionitis is diagnosed clinically in the setting of Maternal fever (≥ 100.4 °F) and at least two of the following:

- Maternal leukocytosis (> 15,000 cells/mm³)

- Maternal tachycardia (> 100 bpm)

- Fetal tachycardia (> 160 bpm)

- Uterine tenderness

- Foul odor of amniotic fluid

Exclusions:

- Maternal upper respiratory infection.

- Maternal urinary tract infection.

The disease primarily affects older adults, persons with weakened immune systems, pregnant women, and newborns. Rarely, people without these risk factors can also be affected. A person with listeriosis usually has fever and muscle aches, often preceded by diarrhea or other gastrointestinal symptoms. Almost everyone who is diagnosed with listeriosis has invasive infection (meaning that the bacteria spread from their intestines to their blood stream or other body sites). Disease may occur as much as two months after eating contaminated food.

The symptoms vary with the infected person:

- High-risk persons other than pregnant women: Symptoms can include fever, muscle aches, headache, stiff neck, confusion, loss of balance, and convulsions.

- Pregnant women: Pregnant women typically experience only a mild, flu-like illness. However, infections during pregnancy can lead to miscarriage, stillbirth, premature delivery, or life-threatening infection of the newborn.

- Previously healthy persons: People who were previously healthy but were exposed to a very large dose of Listeria can develop a non-invasive illness (meaning that the bacteria have not spread into their blood stream or other body sites). Symptoms can include diarrhea and fever.

If an animal has eaten food contaminated with Listeria and does not have any symptoms, most experts believe that no tests or treatment are needed, even for people at high risk for listeriosis.

"Ureaplasma urealyticum" is a species in the genus "Ureaplasma" that can cause infection. Though most bacteria possess a cell wall, "U urealyticum" does not. It is found in about 70% of sexually active humans. It can be found in cultures in cases of pelvic inflammatory disease and is transmitted through sexual activity or from mother to infant during birth. It is not a commensal of the healthy uterine or amniotic microbiome. Infection with "U. realyticum" can contribute neonatal infection and negative birth outcomes.

An intercurrent (or concurrent, concomitant or, in most cases, pre-existing) disease in pregnancy is a disease that is not directly caused by the pregnancy (in contrast to a complication of pregnancy), but which may become worse or be a potential risk to the pregnancy (such as "causing" pregnancy complications). A major component of this risk can result from necessary use of drugs in pregnancy to manage the disease.

In such circumstances, women who wish to continue with a pregnancy require extra medical care, often from an interdisciplinary team. Such a team might include (besides an obstetrician) a specialist in the disorder and other practitioners (for example, maternal-fetal specialists or obstetric physicians, dieticians, etc.).

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.

Though GBS colonization is asymptomatic and, in general, does not cause problems, it can sometimes cause serious illness for the mother and the baby during gestation and after delivery. GBS infections in the mother can cause chorioamnionitis (intra-amniotic infection or severe infection of the placental tissues) infrequently, and postpartum infections (after birth). GBS urinary tract infections may induce labour and cause premature delivery (preterm birth) and miscarriage.

Most people infected with trichomonas vaginalis do not have any symptoms and can be undetected for years. Symptoms experienced include pain, burning or itching in the penis, urethra (urethritis), or vagina (vaginitis). Discomfort for both sexes may increase during intercourse and urination. For women there may also be a yellow-green, itchy, frothy, foul-smelling ("fishy" smell) vaginal discharge. In rare cases, lower abdominal pain can occur. Symptoms usually appear within 5 to 28 days of exposure.

Signs in mares appear ten to fourteen days after breeding to an infected or carrier stallion. A gray to creamy vulvar discharge mats the hair of the buttocks and tail, although in many cases, the discharge is absent and the infection is not apparent. Most mares recover spontaneously, although many become carriers. Infected mares are usually infertile during the acute illness. However, the infertility only lasts a few weeks, after which pregnancy is possible.

Stallions do not show signs of infection. The first indication of the carrier state is lack of pregnancy in the mares covered by the stallion.

GBS is found in the gastrointestinal and genitourinary tract of humans. In different studies, GBS vaginal colonization rate ranges from 4 to 36%, with most studies reporting rates over 20%. These variations in the reported prevalence of asymptomatic (presenting no symptoms of disease) colonization could be related to the different detection methods used, and differences in populations studied.

Though GBS is an asymptomatic colonizer of the gastrointestinal human tract in up to 30% of otherwise healthy adults, including pregnant women,

this opportunistic harmless bacterium can, in some circumstances, cause severe invasive infections.

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.

Acute toxoplasmosis is often asymptomatic in healthy adults. However, symptoms may manifest and are often influenza-like: swollen lymph nodes, headaches, fever, and fatigue, or muscle aches and pains that last for a month or more. Rarely will a human with a fully functioning immune system develop severe symptoms following infection. People with weakened immune systems are likely to experience headache, confusion, poor coordination, seizures, lung problems that may resemble tuberculosis or Pneumocystis jiroveci pneumonia (a common opportunistic infection that occurs in people with AIDS), or blurred vision caused by severe inflammation of the retina (ocular toxoplasmosis) Young children and immunocompromised people, such as those with HIV/AIDS, those taking certain types of chemotherapy, or those who have recently received an organ transplant, may develop severe toxoplasmosis. This can cause damage to the brain (encephalitis) or the eyes (necrotizing retinochoroiditis). Infants infected via placental transmission may be born with either of these problems, or with nasal malformations, although these complications are rare in newborns. The toxoplasmic trophozoites causing acute toxoplasmosis are referred to as tachyzoites, and are typically found in bodily fluids.

Swollen lymph nodes are commonly found in the neck or under the chin, followed by the armpits and the groin. Swelling may occur at different times after the initial infection, persist, and recur for various times independently of antiparasitic treatment. It is usually found at single sites in adults, but in children, multiple sites may be more common. Enlarged lymph nodes will resolve within one to two months in 60% of cases. However, a quarter of those affected take two to four months to return to normal, and 8% take four to six months. A substantial number (6%) do not return to normal until much later.

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