What Is Triploidy

Introduction

Triploidy (also known as chromosome triploidy syndrome/triploid syndrome/triploidy syndrome) is an uncommon genetic abnormality that results in a developing fetus to have an additional set of chromosomes in the cell making a total of 69 chromosomes instead of the usual 46 chromosomes per cell. This is one of the most prevalent chromosome disorders in humans affecting approximately 1-2% of all conceptions and causing 10% of all spontaneous abortions.¹ Continue reading to find out more about the causes, types, diagnosis, symptoms and treatment of this genetic disorder.

Causes and types of triploidy

The majority of triploidy cases feature "full" triploidy, in which all of the body's cells are uniformly impacted. Rarely, triploidy can be "mosaic," meaning that some of the body's cells contain three copies of each chromosome while others have the typical 46 chromosomes.² There is some evidence to suggest that people with mosaic triploidy may experience the disorder less severely than people with full triploidy. Nevertheless, the outlook is poor even with mosaic triploidy.³

The extra pair of chromosomes is produced during fertilization by either the mother or the father. Hence, triploidy can be caused by two different forms of abnormal fertilization⁴:

• Digynic fertilization (in which the mother provides the extra set of chromosomes) is a process of the fertilization of an egg with multiple chromosomes by a regular sperm
• Diandric fertilization (in which the father provides the extra set of chromosomes) is achieved when two sperm fertilize a single egg or when a sperm with an additional set of chromosomes fertilizes an egg

Dyginic embryos have a higher likelihood of making it to the second trimester of pregnancy or even baby delivery.^4-6

Triploidy typically occurs infrequently or randomly and is unrelated to family history or the parent's age at the time of conception.

Diagnosis of Triploidy

Prenatal diagnosis

The most crucial information regarding the genetic health of the fetus is obtained through prenatal diagnostics performed using non-invasive testing (such as biochemical and ultrasound examinations) during the first and second trimesters of pregnancy.⁷

Prenatal tests to confirm a diagnosis include:

• An ultrasound is a type of imaging procedure that enables the healthcare professional to see the fetus inside of the uterus. The doctor can examine for congenital growth abnormalities and condition symptoms using an ultrasound. Because the sonographic characteristics of pregnancies complicated by fetal triploidy vary, ultrasound alone cannot be used to make the diagnosis.⁸
• Amniocentesis: To check for chromosome abnormalities, a healthcare professional will take a small sample of the patient’s amniotic fluid.
• Chorionic villus sampling: The doctor will use a needle to take a tiny sample of the placenta to check for chromosomal abnormalities.

Postnatal diagnosis

A genetic test, which uses a small sample of the baby's blood to detect alterations to their chromosomes, can be used to diagnose triploidy postnatally. Only a chromosome analysis (karyotype) test will confirm whether a person is triploid. Soon after birth, a physical examination is performed to make the diagnosis in newborns. The initial signs of triploidy include physical birth abnormalities, aberrant placenta, and severe growth retardation.

Symptoms and clinical presentation

Prenatal Symptoms

The majority of babies with triploidy—more than 99%—are stillborn or miscarried.⁹

Symptoms that could influence a fetus's development in the uterus and that are associated with triploidy include:

• Convulsions brought on by abnormal brain development
• Adrenal and kidney defects
• Abnormalities of the face, including widely-spaced eyes, low nasal bridge, low-set malformed ears, small jaw, and a cleft lip and palate
• Merged toes and fingers
• Short stature
• Anomalies in the growth of the gallbladder, liver, spinal cord, and intestines
• Heart defects

Triploidy can also affect the pregnant woman and result in symptoms such as:

• Placenta that is usually large, immature, and filled with cysts
• Swelling (edema)
• Increased blood pressure
• Urinary albumin excretion

Postnatal symptoms

Newborns that are affected by triploidy typically have severe growth limitation and multiple birth abnormalities including:

• Microcephalic head with a large posterior fontanelle and fuzzy hair¹⁰
• Eears with tiny tragi and bilaterally unfolded helices¹⁰
• Bilateral vertically ovoid corneae and coloboma of the left iris¹⁰
• Large feet with prominent heels¹⁰
• Abnormalities in the genitalia¹⁰

Management and treatment

Prenatal diagnosis of congenital abnormalities and genetic counseling rank among the most significant advancements in preventive medicine in the last century.¹¹ If triploidy was diagnosed prenatally, the carrying mother will likely be asked if she wants to carry on with the pregnancy. Making the difficult and personal decision to proceed with the pregnancy or not is very difficult. Certain changes in the placenta may indicate to healthcare professionals that the woman may experience pre-eclampsia in the middle of the pregnancy. This is a highly serious and possibly fatal problem, therefore it is something to take into account when making this extremely tough choice. Generally, women who are not yet 14 weeks pregnant are given the option of a suction curettage performed under general anesthesia or a D&C (dilatation and curettage, also referred to as D& E - evacuation). After 14 weeks, the woman will undergo labor after being given a prostaglandin induction.¹²

Because the outcome is inevitable, extra procedures like fetal monitoring or a caesarean section are not necessary based only on the diagnosis of triploidy. Although the majority of babies with triploidy pass away before they are born, some do survive for a few hours, days, or weeks after delivery. Some survive for a few months.

Reducing a baby's life-threatening symptoms is the main goal of treatment after they are born. This could involve supportive care to enable them to live comfortably, or a surgery or medication to address congenital growth problems. However, sometimes, comfort care is advised instead of pursuing any kind of rigorous intervention.

Prognosis and long-term outlook

Miscarriages occur in the vast majority of triploid pregnancies and they make up roughly 20% of all spontaneous abortuses caused by genetic abnormalities.¹³ The live birth rate of all cases of triploidy is 1/10,000 live births, and the offspring are profoundly mentally impaired. In most cases, triploidy causes fetal death in utero. There are no live birth survivors known to have survived longer than 10.5 months.¹³

Triploidy may cause recurrent miscarriages in a small percentage of cases.³ The total risk of recurrence of digynic triploid pregnancies has not been determined, despite reports of several recurrences exist.¹⁴ The recurrence risk for diandric triploid pregnancies is around double that of the general population.¹⁵

The optimal period of time to wait before attempting for another child is not set in stone. Usually, women who are monitored for two years following a partial molar pregnancy are told to hold off until six months after receiving normal findings from their blood and urine tests.¹²

FAQ

What is the difference between trisomy and triploidy?

Trisomy and triploidy are not the same thing. Individuals who have trisomy have an additional chromosome, for a total of 47. The most well-known type of trisomy is Down's syndrome, which is caused by an extra copy of chromosome 21. 

Is triploidy caused by something that the parent(s) may or may not have done?

Triploidy is an occasional (or accidental) event. It is not the result of anything a parent has done or hasn't done. In contrast to certain other chromosomal abnormalities (such as Downs syndrome or trisomy 21), triploidy is unrelated to the age of the mother. This indicates that an older mother's pregnancy does not have a higher risk of triploidy.¹⁶

Can triploidy happen when undergoing in vitro fertilisation (IVF)?

In a case report presented by Pal et al. (1996), it was found that using oocytes from a patient who had experienced recurrent gestational trophoblastic disease (GTD) in vitro fertilization (IVF) resulted in a noticeably high prevalence of triploid embryos.¹⁷

Is triploidy hereditary?

Triploidy is not hereditary. There is no increased risk of triploidy in subsequent pregnancies for a couple who has had one affected pregnancy.

How early can triploidy be detected on ultrasound?

Fetal triploidy can show up as molar abnormalities in the placenta or as a cluster of odd ultrasound findings between weeks 12 and 16 of pregnancy.¹⁸

In which week of pregnancy does a triploid miscarriage usually occur?

Most triploid fetuses are spontaneously miscarried between week seven and week seventeen of gestation.¹⁹

Summary

A lethal genetic disorder known as triploidy occurs when a fetus receives an additional pair of chromosomes from one of its parents - either the mother (digynic fertilization) or the father (diandric fertilization). About 1-2% of conceptions result in triploidy; nevertheless, the majority of these pregnancies terminate spontaneously at an early stage. Although infants with mosaic triploidy—two cell lines, one normal and one triploid—often survive pregnancy, they typically suffer from severe mental impairment, various birth deformities, and severe growth abnormalities. In contrast to certain other chromosomal abnormalities (such as Downs syndrome or trisomy 21), triploidy is unrelated to the age of the mother. The diagnosis of triploidy is made either prenatally or postnatally. The condition is treated with supportive and symptomatic measures. Joining a support group could be beneficial if the parents are having trouble processing their emotions. It can also be helpful to find a therapist or counselor that specializes in pregnancy loss.