**Core Concept**
Intestinal obstruction in newborns is a medical emergency that can be caused by various factors, including anatomical abnormalities, volvulus, and intussusception. The common causes of intestinal obstruction in newborns are often related to congenital anomalies or acquired conditions that occur during fetal development or shortly after birth.

**Why the Correct Answer is Right**
The commonest cause of intestinal obstruction in newborns is duodenal atresia. This condition occurs when there is a complete or partial closure of the duodenum, which is the first portion of the small intestine. Duodenal atresia is often associated with other congenital anomalies, such as trisomy 21 (Down syndrome), and is typically diagnosed on prenatal ultrasound or shortly after birth. The obstruction can be relieved through surgical intervention, such as duodeno-duodenostomy or duodenojejunostomy.

**Why Each Wrong Option is Incorrect**
* **Option A:** Intussusception is a common cause of intestinal obstruction in infants and children, but it is relatively rare in newborns. Intussusception occurs when a segment of intestine telescopes into another, leading to bowel obstruction.
* **Option B:** Volvulus, or twisting of the intestine, is another cause of intestinal obstruction, but it is not as common as duodenal atresia in newborns. Volvulus can be caused by various factors, including congenital anomalies or acquired conditions.
* **Option D:** Meconium ileus is a condition that occurs when meconium is inspissated and blocks the ileum, but it is more commonly seen in infants with cystic fibrosis.

**Clinical Pearl / High-Yield Fact**
Newborns with intestinal obstruction often present with bilious vomiting, abdominal distension, and failure to pass meconium within the first 24 hours of life. Duodenal atresia is often associated with a "double-bubble" sign on abdominal radiograph, which is a characteristic feature of this condition.

**Correct Answer: D. Meconium ileus