Labial fusion is not uncommon in infants and young girls. It is most common in infants between the ages of 13 and 23 months, and has an incidence of 3.3% in this age group. It is estimated that labial fusion occurs in 1.8% of all prepubertal girls. It is rare in adult women, particularly in reproductive age, but is occasionally found in postpartum and postmenopausal women.

Webbed penis, also called penis palmatus or penoscrotal fusion, is an acquired or congenital condition in which the scrotal skin extends onto the ventral penile shaft. The penile shaft is buried in scrotum or tethered to the scrotal midline by a fold or web of skin. The urethra and erectile bodies are usually normal. Webbed penis is usually asymptomatic, but the cosmetic appearance is often unacceptable. This condition may be corrected by surgical techniques.

In the congenital form, the deformity represents an abnormality of the attachment between the penis and the scrotum; the penis, the urethra, and the remainder of the scrotum typically are normal.

Webbed penis may also be acquired (iatrogenic) after circumcision or other penile surgery, resulting from excessive removal of ventral penile skin; the penis can retract into the scrotum, resulting in secondary phimosis (trapped penis).

One procedure for webbed penis is the insertion of a subcutaneous soft silicone implant under the penile skin. The procedure was developed by urologist James J. Elist.

The primary contributing factor to labial fusion is low estrogen levels. A vulva with low estrogen exposure, such as that of a preadolescent, has delicate epithelial lining and is therefore vulnerable to irritation. Conditions causing irritation, such as infection, inflammation and trauma, cause the edges of the labia minora to fuse together. The fusion typically begins at the posterior frenulum of the labia minora and continues anteriorly.

Most labial adhesions resolve spontaneously before puberty as estrogen levels increase and the vaginal epithelium becomes cornified.

Hypospadias is among the most common birth defects in the world and is said to be the second-most common birth defect in the male reproductive system, occurring once in every 250 males.

Due to variations in the reporting requirements of different national databases, data from such registries cannot be used to accurately determine either incidence of hypospadias or geographical variations in its occurrences.

Pregnancies in a bicornuate uterus are usually considered high risk and require extra monitoring because of association with poor reproduction potential.

A bicornuate uterus is associated with increased adverse reproductive outcomes, such as:

- Recurrent pregnancy loss

- Preterm birth: The rate of preterm delivery is 15 to 25%. A pregnancy may not reach full term in a bicornuate uterus when the baby begins to grow in either of the uterine horns. A short cervical length seems to be a good predictor of preterm delivery in women with a bicornuate uterus.

- Malpresentation (breech birth or transverse presentation): a breech presentation occurs in 40-50% of pregnancies with a partial bicornuate uterus and not at all (0%) in a complete bicornuate uterus.

- Deformity: Offspring of mothers with a bicornuate uterus are at high risk for "deformities and disruptions" and "malformations."

Previously, a bicornuate uterus was thought to be associated with infertility, but recent studies have not confirmed such an association.

The occurrence of all types of paramesonephric duct abnormalities in women is estimated around 0.4%.

A bicornuate uterus is estimated to occur in 0.1-0.5% of women in the U.S.

It is possible that this figure is an underestimate, since subtle abnormalities often go undetected. Some intersex individuals whose external genitalia are perceived as being male may nonetheless have a variably shaped uterus.

While most hypospadias repairs are done in childhood, occasionally, an adult was not operated and then desires surgery because of urinary spraying or unhappiness with the appearance. Other adults wanting surgery have complications that were never fully corrected during childhood.

Generally, operations done on adults are less successful than those in children. So, some adults have been discouraged from having corrective surgery. However, a direct comparison of surgical results in children versus adults found they had the same outcomes, and adults can undergo hypospadias repair or reoperations with good expectations for success.

Most studies are based on populations of women who have experienced a pregnancy loss and thus do not address the issue of the prevalence in the general population. A screening study by Woelfer et al. of women without a history of reproductive problems found that about 3% of women had a uterine septation; the most common anomaly in their study was an arcuate uterus (5%), while 0.5% were found to have a bicornuate uterus. In contrast, in about 15% of patients with recurrent pregnancy loss anatomical problems are thought to be causative with the septate uterus as the most common finding.

In the United States, uterus didelphys is reported to occur in 0.1–0.5% of women. It is difficult to know the exact occurrence of this anomaly, as it may go undetected in the absence of medical and reproductive complications.

In most cattle twins, the blood vessels in the chorions become interconnected, creating a shared circulation for both twins. If both fetuses are the same sex this is of no significance, but if they are different, male hormones pass from the male twin to the female twin. The male hormones (testosterone and anti-Müllerian hormone) then masculinize the female twin, and the result is a freemartin. The degree of masculinization is greater if the fusion occurs earlier in the pregnancy – in about ten percent of cases no fusion takes place and the female remains fertile.

The male twin is largely unaffected by the fusion, although the size of the testicles may be slightly reduced. Testicle size is associated with fertility, so there may be some reduction in bull fertility.

Freemartins behave and grow in a similar way to castrated male cattle (steers).

A number of twin gestations have occurred where each uterus carried its pregnancy separately. A recent example occurred on February 26, 2009, when Sarah Reinfelder of Sault Ste. Marie, Michigan delivered two healthy, although seven weeks premature, infants by cesarean section at Marquette General Hospital. It is possible that the deliveries occur at different times, thus the delivery interval could be days or even weeks.

A freemartin is the normal outcome of mixed twins in all cattle species which have been studied. It does not normally occur in most other mammals, though it has been recorded in sheep, goats, pigs, deer, and camels.

The condition may not be known to the affected individual and not result in any reproductive problems; thus normal pregnancies may occur. However, it is associated with a higher risk for miscarriage, premature birth, and malpresentation. According to the classical study by Buttram there is a 60% risk of a spontaneous abortion, this being more common in the second than in the first trimester. However, there is no agreement on this number and other studies show a lower risk. Woelfer found that the miscarriage risk is more pronounced in the first trimester.

The condition is also associated with abnormalities of the renal system. Further, skeletal abnormalities have been linked to the condition.

Most studies of uterine malformations are based on populations of women who have experienced a pregnancy loss and thus do not address the issue of the prevalence in the general population. A screening study by Woelfer et al. of women without a history of reproductive problems found that about 5% of women had an arcuate uterus when they defined an arcuate uterus any fundal protrusion into the cavity that had an apical angle of more than 90 degrees. Accordingly, it was the most common uterine anomaly, followed by septate uterus (3%) and bicornuate uterus (0.5%).

The condition may not be known to the affected individual and not result in any reproductive problems; thus normal pregnancies occur. Indeed, there is no consensus on the relationship of the arcuate uterus and recurrent pregnancy loss. Accordingly, the condition may be a variation or a pathology.

One view maintains that the condition is associated with a higher risk for miscarriage, premature birth, and malpresentation. Thus a study that evaluated women with uterine bleeding by hysteroscopy found that 6.5% of subjects displayed the arcuate uterus and had evidence of reproductive impairments. A study based on hysterosalpingraphic detected arcuate lesions documented increased fetal loss and obstetrical complications as a risk for affected women. Woelfer found that the miscarriage risk is more pronounced in the second trimester. In contrast, a study utilizing 3-D ultrasonography to document the prevalence of the arcuate uterus in a gynecological population found no evidence of increased risk of reproductive loss; in this study 3.1% of women had an arcuate uterus making it the most common uterine anomaly; this prevalence was similar than in women undergoing sterilization and lower than in women with recurrent pregnancy loss.

Hand-foot-genital syndrome is inherited in an autosomal dominant manner. The proportion of cases caused by de novo mutations is unknown because of the small number of individuals described. If a parent of the proband is affected, the risk to the siblings is 50%. When the parents are clinically unaffected, the risk to the sibs of a proband appears to be low. Each child of an individual with HFGS has a 50% chance of inheriting the mutation. Prenatal testing may be available through laboratories offering custom prenatal testing for families in which the disease-causing mutation has been identified in an affected family member.

Diagnosis is based on physical examination including radiographs of the hands and feet and imaging studies of the kidneys, bladder, and female reproductive tract. HOXA13 is the only gene known to be associated with HFGS. Approximately 60% of mutations are polyalanine expansions. Molecular genetic testing is clinically available.

Midline cervical clefts are a rare congenital anomaly resulting from incomplete fusion during embryogenesis of the first and second branchial arches in the ventral midline of the neck. The condition presents as a midline cutaneous defect of the anterior neck with a skin projection or sinus, or as a subcutaneous erythematous fibrous cord. Surgical excision is the preferred treatment.

The prevalence of Klippel–Feil syndrome is unknown due to the fact that there was no study done to determine the true prevalence.

Although the actual occurrence for the KFS syndrome is unknown, it is estimated to occur 1 in 40,000 to 42,000 newborns worldwide. In addition, females seem to be affected slightly more often than males.

Splenogonadal fusion is a rare congenital malformation that results from an abnormal connection between the primitive spleen and gonad during gestation. A portion of the splenic tissue then descends with the gonad. Splenogonadal fusion has been classified into two types: continuous, where there remains a connection between the main spleen and gonad; and discontinuous, where ectopic splenic tissue is attached to the gonad, but there is no connection to the orthotopic spleen. Patients with continuous splenogonadal fusion frequently have additional congenital abnormalities, most commonly cryptorchidism.

The anomaly was first described in 1883 by Bostroem. Since then more than 150 cases of splenogonadal fusion have been documented. The condition is considered benign. A few cases of testicular neoplasm have been reported in association with splenogonadal fusion. The reported cases have occurred in patients with a history of cryptorchidism, which is associated with an elevated risk of neoplasm.

Splenogonadal fusion occurs with a male-to-female ratio of 16:1, and is seen nearly exclusively on the left side. The condition remains a diagnostic challenge, but preoperative consideration of the diagnosis may help avoid unnecessary orchiectomy. On scrotal ultrasound, ectopic splenic tissue may appear as an encapsulated homogeneous extratesticular mass, isoechoic with the normal testis. Subtle hypoechoic nodules may be present in the mass. The presence of splenic tissue may be confirmed with a technetium-99m sulfur colloid scan.

A median mandibular cyst is a type of cyst that occurs in the midline of the mandible, thought to be created by proliferation and cystic degeneration of resting epithelial tissue that is left trapped within the substance of the bone during embryologic fusion of the two halves of the mandible, along the plane of fusion later termed the symphysis menti. A ture median mandibular cyst would therefore be classified as a non-odontogenic, fissural cyst. The existence of this lesion as a unique clinical entity is controversial, and some reported cases may have represented misdiagnosed odontogenic cysts, which are by far the most common type of intrabony cyst occurring in the jaws. It has also been suggested that the mandible develops as a bilobed proliferation of mesenchyme connected with a central isthmus. Therefore, it is unlikely that epithelial tissue would become trapped as there is no ectoderm separating the lobes in the first instance.

Sternal clefts are rare congenital malformations that result from defective embryologic fusion of paired mesodermal bands in the ventral midline. They may be associated with other midline defects (as in pentalogy of Cantrell). It may also occur in isolation. Sternal cleft is treated by surgery in early life to avoid fixation leading to immobility.

The heterogeneity of the Klippel–Feil syndrome has made it difficult to outline the diagnosis as well as the prognosis classes for this disease. Because of this, it has complicated the exact explanation of the genetic cause of the syndrome.

The prognosis for most individuals with KFS is good if the disorder is treated early on and appropriately. Activities that can injure the neck should be avoided, as it may contribute to further damage. Other diseases associated with the syndrome can be fatal if not treated, or if found too late to be treatable.

Surgery is needed to prevent the closing of the coronal sutures from damaging brain development. In particular, surgeries for the LeFort III or monobloc midface distraction osteogenesis which detaches the midface or the entire upper face, respectively, from the rest of the skull, are performed in order to reposition them in the correct plane. These surgeries are performed by both plastic and oral and maxillofacial (OMS) surgeons, often in collaboration.

Omphalocele has been described in two patients with Apert syndrome by Herman T.E. et al. (USA, 2010) and by Ercoli G. et al. (Argentina, 2014). An omphalocele is a birth defect in which an intestine or other abdominal organs are outside of the body of an infant because of a hole in the bellybutton area. However, the association between omphalocele and Apert syndrome is not confirmed yet, so additional studies are necessary.