Congenital anomalies include structural and functional adverse conditions present at birth or developing later in life, significantly affecting health and development. These defects range from minor physical malformations to severe impairments requiring extensive medical intervention. Structural anomalies, such as congenital heart defects and cleft lip and palate, affect physical formation, while functional defects impact bodily systems, including metabolic and neurological disorders [1, 2]. The prevalence of birth defects varies across populations due to genetic, environmental, and socio-economic factors, influencing both affected families and public health systems.

Infants classified as small for gestational age (SGA) weigh below the 10th percentile for their gestational age, indicating restricted growth in utero. This condition stems from maternal, placental, and fetal factors and often leads to serious health complications immediately after birth and throughout life. In 2020, an estimated 23 million live births – approximately 17% of all births worldwide – met the criteria for SGA, with the highest prevalence in southern Asia and sub-Saharan Africa, where rates reach up to 41% [3]. 

Various factors contribute to SGA, including maternal health conditions (such as hypertension and diabetes), lifestyle choices (like smoking and substance use), placental dysfunction, and fetal development. Soci-oeconomic status also plays a crucial role, as lower income levels correlate with higher SGA risk due to inadequate nutrition and healthcare access [4-6]. 

SGA infants face increased risks of developmental delays, chronic health conditions, and higher mortality rates. Addressing these risks requires a multifaceted approach, including improved maternal healthcare access, education, and community-based interventions that target social determinants of health [5, 7].

Maternal health significantly affects fetal growth and the likelihood of SGA. Conditions such as hypertension, diabetes, and chronic kidney disease contribute to placental insufficiency, limiting nutrient and oxygen supply to the fetus [5, 8]. Additionally, maternal lifestyle choices, including smoking, alcohol use, and substance abuse (such as opioids or cocaine), reduce fetal growth and increase SGA risk [8, 9]. Poor maternal nutrition also raises the likelihood of SGA, as underweight mothers or those with a low body mass index (BMI) face higher risks of delivering small infants [8].

Fetal growth restriction, also known as intrauterine growth restriction (IUGR), can result from genetic disorders or congenital infections. IUGR is classified as symmetric (affecting overall fetal size) or asymmetric (primarily affecting body weight while sparing head growth) [8]. Asymmetric IUGR often results from inadequate fetal nutrition, where prenatal circulation prioritizes brain development over body weight. Early identification of IUGR is crucial, as it may require closer monitoring or early delivery if fetal well-being is at risk [8, 9].

The placenta plays a vital role in fetal development by facilitating the exchange of nutrients and oxygen between mother and fetus. Placental insufficiency, often caused by maternal health issues or multiple pregnancies, can result in asymmetric growth restrictions where the head circumference remains unaffected, but body weight is significantly reduced [8, 9]. Structural or functional abnormalities in the placenta may further impair fetal growth. Healthcare providers typically diagnose placental insufficiency through ultrasound and Doppler studies, which assess blood flow and identify abnormalities contributing to SGA [8]. 

Structural birth anomalies are physical abnormalities that occur during fetal development and are present at birth, affecting various body systems and functions. Beyond their impact on individual families, these conditions pose significant public health concerns, as they can lead to lifelong disabilities, increased healthcare costs, and the need for specialized medical care. Common structural birth anomalies include abdominal wall defects, congenital heart defects, limb deficiencies, neural tube defects, and orofacial clefts. Genetic and environmental factors often contribute to these conditions, making prevention, specialized prenatal care, and interdisciplinary treatment essential for improving outcomes [10, 11]. 

Abdominal wall defects, such as gastroschisis and omphalocele, cause intestines and other organs to protrude outside the body due to incomplete closure of the abdominal wall. Ultrasound examinations during pregnancy typically detect these conditions, allowing for early diagnosis. Surgical intervention shortly after birth is necessary to correct the defect and prevent complications [12, 13]. 

Congenital heart defects rank among the most common structural birth anomalies, affecting approximately 18 out of every 1,000 births worldwide [14]. These defects alter the heart’s chambers, valves, or blood vessels, impairing its ability to pump blood efficiently. Common congenital heart defects include ventricular septal defects, atrial septal defects, and Tetralogy of Fallot. Genetic predisposition and environmental factors, such as maternal exposure to certain medications or infections during pregnancy, contribute to these conditions [10, 13].

Limb deficiencies result in missing or underdeveloped limbs and include conditions like clubfoot, where the foot twists inward. The severity of these defects varies, and prenatal diagnosis is sometimes possible. Genetic and environmental factors often play a role in their development [13, 15]. 

Neural tube defects occur when the neural tube, which forms the brain and spinal cord, fails to close properly within the first month of embryonic development. The most recognized neural tube defects include: 

• Spina Bifida: The spinal cord and vertebrae do not close completely, potentially causing partial or complete paralysis of the lower limbs. 
• Anencephaly: A fatal condition where a major part of the brain does not develop. 

Approximately 1 in every 1,500 live births is affected by an neural tube defect, with spina bifida being the most common form. These defects can lead to significant physical and neurological complications [10, 11]. 

Orofacial clefts, including cleft lip and cleft palate, occur when tissues in the face and mouth fail to fuse properly during early embryonic development. These conditions affect approximately 1 in 700 live births, leading to challenges with feeding, speech development, and dental health. Early surgical intervention and multidisciplinary care help improve functional and cosmetic outcomes [12, 13].

Functional birth anomalies encompass a wide range of congenital conditions that affect a child's physical, cognitive, and behavioral development. These complications often impact an individual's quality of life and pose significant healthcare challenges. Functional birth defects fall into several categories, including developmental, genetic, and those caused by maternal infections or environmental exposures [16, 17]. 

Developmental complications affect cognitive and behavioral skills, leading to challenges in communication, movement, and muscle tone. Autism spectrum disorders (ASD) and cerebral palsy are among the most well-known conditions in this category. These disorders often become noticeable as children grow, rather than immediately after birth [18-20]. 

Genetic factors play a major role in functional birth anomalies. Conditions such as Down syndrome and cystic fibrosis result from inherited genetic abnormalities, often causing physical and intellectual disabilities [21]. 

Environmental exposures during pregnancy can significantly increase the risk of functional birth anomalies. Certain industrial chemicals and medications can interfere with fetal development, leading to long-term health issues [22, 23]. Research highlights maternal nutrition, particularly folic acid intake, as a crucial factor in preventing neural tube defects [23, 24]. Early diagnosis and intervention improve outcomes and enhance the quality of life for affected individuals and their families. 

Exposure to harmful substances during pregnancy, including alcohol, tobacco, pesticides, and certain medications, increases the risk of birth defects and developmental disorders. Prenatal alcohol exposure is one of the leading causes of neurodevelopmental disorders and has been linked to conditions such as cleft lip and congenital heart defects [25, 26]. 

One severe consequence of prenatal alcohol exposure is Fetal Alcohol Syndrome (FAS), the most extreme form of Fetal Alcohol Spectrum Disorders (FASD). FAS causes distinctive facial features, growth deficiencies, and lifelong neurodevelopmental impairments, such as intellectual disabilities, attention deficits, and impulse control issues. It affects an estimated 2% to 7% of children worldwide and contributes to significant healthcare and social costs due to the need for lifelong support services [27]. 

Socio-economic status indirectly affects congenital disorder rates. Families with low incomes often struggle with access to nutritious food, prenatal care, and education on avoiding harmful substances, increasing the prevalence of birth defects. Approximately 94% of severe congenital disorders occur in low- and middle-income countries, where these challenges are more prevalent [17].