Introduction

Triploidy is an anomaly resulting from an extra set of chromosomes in each cell. Chromosomes are the housing for our DNA and genes that determine everything from physical appearance to bodily functions. In our cells, we usually have 46 chromosomes: 22 pairs of autosomes and one pair of sex chromosomes (23 pairs of chromosomes from each parent).¹ In triploidy, the extra chromosome causes 69 chromosomes to be present, resulting in the life-threatening condition.² 

Triploidy is one of the most common chromosomal abnormalities, with a prevalence of only 1-3% among new pregnancies. It accounts for approximately 10% of chromosomal abnormalities found in first-trimester miscarriages and about 0.002% of viable pregnancies between 16 and 20 weeks of gestation.^2,3 

This condition is not hereditary, so it doesn’t pass along through family generations and is not associated with parental age. As the condition leads to numerous severe congenital abnormalities, early spontaneous abortion or miscarriage is extremely common. However, occasionally the pregnancy is viable, and an abnormal foetus or baby can develop and be born.^1,4 

Causes of triploidy 

Triploidy is a result of:¹

• Genetic mutations – variations created by hereditary, viral, environmental or physiological factors
• Chromosomal changes – a change in the normal chromosome count or a change in their structure, particularly the addition of an entire extra haploid set 

Mechanisms of triploidy formation and its types

In triploidy, the additional chromosomal set found can either be received by the father (diandric triploidy) or the mother (digynic triploidy). The phenotype, that is, our appearance and traits, is influenced by the origin of the chromosome set.³ 

 Three different types of karyotypes that are possible with triploidy. These are:³

1. 69, XXX – chromosomal set inherited by mother or father 
2. 69, XXY – chromosomal set inherited by mother or father 
3. 69, XYY – chromosomal set inherited by father 

Diandric triploidy

Diandry results when two sperm fertilise one egg (dispermy) or a single diploid (2n) sperm fertilises a haploid (n) egg. This type is commonly associated with partial hydatidiform mole (PHM), characterised by a large, cystic placenta and an absent or underdeveloped embryo.^3,4 

It appears mainly in pregnancies of gestational age greater than 8.5 weeks and greater than 10 weeks with no embryo or foetus detected and is responsible for 50-60% of early triploid spontaneous abortions. Notably, these foetuses are distinguished by normal proportions or mildly symmetrical growth retardation along with normal adrenal glands. The risk of complications such as gestational trophoblastic neoplasia (GTN) is higher in these cases.^3,4

Digynic triploidy

Digyny arises when a diploid egg is fertilised by a haploid sperm. This usually results from meiotic errors during oogenesis. Less commonly, it may occur from the fusion of two haploid oocytes or the failure of nuclear division, producing a giant diploid oocyte.^3,4  

This type of triploidy occurs largely in pregnancies younger than 8.5 weeks gestational age or 10 weeks gestational age, where embryos are present. Pregnancies affected have a higher viability compared to those affected by diandry, so viable triploid foetuses in the second or third trimester are normally digynic in nature. The foetuses are characterised by distinct asymmetric intrauterine growth restriction (IUGR), underdeveloped adrenal glands and a small, non‐molar placenta.^3,4

Clinical features

In triploidy, there is much to be considered about its presentations. Read on to learn more. 

Maternal symptoms and complications

The mother may experience the following symptoms while being pregnant with a triploid foetus:^1,2,3 

• Vaginal bleeding or spotting
• Severe nausea and vomiting (hyperemesis gravidarum)
• Fluid build-up 
• Theca lutein ovarian cysts (in diandric triploidy)
• Gestational hypertension (in diandric triploidy)
• Early-onset pre-eclampsia (in diandric triploidy)
• Increased risk of partial hydatidiform mole (PHM)
• Increased risk of gestational trophoblastic neoplasia (GTN) 

Ultrasound findings

An ultrasound can show distinct defects relating to the placenta and foetus. Common findings include:^1,2,3 

• Cystic or molar placenta (in diandric triploidy)
• Undersized  or underdeveloped placenta (in digynic triploidy)
• Severe, often asymmetric, intrauterine growth restriction (IUGR)
• Structural defect in the foetus
• Increased nuchal translucency (in diandric triploidy)
• Oligohydramnios or polyhydramnios (amniotic fluid anomalies)

Foetal anomalies

The foetus can be affected in multiple ways and present in several body systems. These symptoms vary in frequency from uncommon to ever-present.^1,2,3 

• Craniofacial abnormalities – acrania, macrocephaly, cleft lip/palate, micrognathia
• Excess fluid accumulation (fetal hydrops) 
• Limb deformities – syndactyly, clubfoot
• Central nervous system defects – cerebellar hypoplasia, holoprosencephaly, hydrocephalus, ventriculomegaly
• Cardiac defects – ventricular and atrioventricular septal defects, transposition of great arteries, cardiomegaly
• Intellectual disability
• Growth abnormalities in the intestines, liver, lungs, pancreas and gallbladder
• Renal abnormalities - cystic kidney disease, renal agenesis, hydronephrosis
• Omphalocele (abnormal wall defects)
• Distinct facial features – narrow mouth, low-set ears, low nasal bridge, short neck, large tongue, cat eye, small eye

Screening and diagnosis 

Ultrasound and imaging scans

Ultrasounds or imaging scans are used to detect any congenital growth or structural anomalies, as well as placental changes. Along with a typical ultrasonography, other scans include:^1,5,6

• Nuchal translucency scan – an optional scan done in the first trimester of pregnancy to measure the amount of fluid that is in the back of the foetus’s neck. It indicates the likelihood of the foetus having a chromosomal or genetic abnormality
• Anomaly scan (20-week- screening scan) - checks for 11 different conditions (structural defects) and assesses the foetus’s growth

Genetic testing

These tests are used to detect and diagnose any genetic conditions and can be recommended if a foetal anomaly is detected during an ultrasound:^1,7,8,9

• Amniocentesis – a common invasive diagnostic test involving removing a sample of amniotic fluid that is later tested to analyse foetal chromosomes
• Chorionic villus sampling (CVS testing) – an optional invasive diagnostic  test done either through the vagina (transcervical) or through the abdomen (transabdominal) where a small sample of the placenta is removed and tested 
• Non-invasive prenatal testing (NIPT) – a noninvasive screening test which samples and tests the mother’s blood to analyse foetal DNA in maternal blood, useful for high-risk screening, though less reliable for detecting triploidy specifically 

Maternal serum screening

A serum test analyses the presence of biochemical markers, namely the free beta subunit of human chorionic gonadotropin (beta-hCG) and pregnancy-associated plasma protein-A (PAPP-A). In diandric triploidy, beta-hCG levels are distinctly increased, while in digyny, both free beta-hCG and PAPP-A levels are very low.³

FAQs

What are the clinical features of triploidy?

Triploidy presents with a range of clinical features that affect both the mother and the foetus. Maternal symptoms may include vaginal bleeding, severe nausea and vomiting, early-onset preeclampsia, gestational hypertension, and an increased risk of partial hydatidiform mole (PHM) or gestational trophoblastic neoplasia (GTN). On ultrasound, triploidy can show abnormalities such as a cystic placenta, a small placenta, and severe intrauterine growth restriction. Fetal anomalies may include craniofacial defects, central nervous system abnormalities, cardiac defects, limb deformities, and renal abnormalities

How do you know if you have triploidy in pregnancy?

Triploidy is typically detected through a combination of ultrasound findings and genetic testing. Ultrasound may reveal abnormalities in foetal development, such as structural defects, abnormal placental appearance, and growth restriction. Maternal serum screening may show abnormal levels of biochemical markers, such as elevated or reduced beta-hCG and PAPP-A levels. A definitive diagnosis is made through genetic testing methods like chorionic villus sampling (CVS) or amniocentesis, which confirm the presence of an extra set of chromosomes. Non-invasive prenatal testing (NIPT) can also indicate a high risk of triploidy, but is less reliable for this condition

How early can triploidy be seen on ultrasound?

Triploidy can be detected on ultrasound as early as the first trimester, often around 10–14 weeks of gestation. Early findings may include increased nuchal translucency, cystic changes in the placenta, and severe intrauterine growth restriction. Anomalies in the fetus and placenta become more evident as the pregnancy progresses, particularly during detailed anomaly scans in the second trimester

What does a baby with triploidy look like?

A baby with triploidy often has multiple congenital abnormalities. Common features include craniofacial defects such as macrocephaly and cleft lip or palate, as well as limb deformities like syndactyly (fusion of fingers or toes) and clubfoot. Other physical anomalies may include central nervous system defects, cardiac abnormalities (e.g., septal defects), and renal defects. Distinctive facial features may include a narrow mouth, low-set ears, a low nasal bridge, and a short neck

Summary

Triploidy is a chromosomal abnormality characterised by the presence of an extra set of chromosomes, resulting in 69 chromosomes per cell instead of the usual 46. It affects approximately 1-3% of pregnancies and is a common cause of first-trimester pregnancy losses. In rare cases, the pregnancy may progress with the development of an abnormal foetus or baby.

The condition arises from genetic mutations or chromosomal changes. Triploidy can result from either diandric triploidy, where the extra chromosomes originate from the father, or digynic triploidy, where they come from the mother. Diandric triploidy typically results from abnormal fertilisation involving two sperm or a diploid sperm, while digynic triploidy occurs due to errors in the cell division, producing a diploid egg. On ultrasound, diandric triploidy often shows a cystic placenta with increased nuchal translucency, while digynic triploidy presents a smaller placenta and significant asymmetric foetal growth restriction.

Maternal symptoms of triploidy include vaginal bleeding, severe nausea, ovarian cysts and preeclampsia. Foetal anomalies commonly observed include craniofacial abnormalities, cardiac and central nervous system defects, limb deformities, renal abnormalities, and intellectual disabilities.

Diagnosis involves ultrasound, maternal serum screening, and genetic tests like CVS or amniocentesis. Triploidy is universally associated with poor prognosis, and most affected pregnancies result in early miscarriage or neonatal death. Prompt recognition and appreciative counselling are essential for management.