Step 1: Understanding the Concept:
Identifying high-risk pregnancies is crucial to reducing maternal and neonatal mortality.
Risk factors include maternal anthropometric measurements (height, weight, BMI), obstetric history (number of pregnancies, birth intervals), and existing medical conditions.
Step 2: Detailed Explanation:
Let us evaluate each parameter to determine if it is a pregnancy risk factor:
- (A) BMI 5 kg/$\text{m^2$:} This falls within the completely normal, healthy weight range ($18.5 - 9\text{ kg/m}^2$), and is not a risk factor.
- (B) Maternal weight $<$ 45 kg: Maternal underweight is a significant risk factor associated with intrauterine growth restriction (IUGR), low birth weight (LBW) infants, and maternal anemia.
- (C) Short stature: A maternal height of less than 145 cm is a major risk factor, as it is often associated with a small, contracted pelvis, increasing the risk of cephalopelvic disproportion (CPD) and obstructed labor.
- (D) Multigravida: Women who have had multiple previous pregnancies (especially grand multigravida, $\ge 5$ pregnancies) are at high risk for uterine atony, postpartum hemorrhage (PPH), placenta previa, and nutritional depletion.
- (E) Birth interval 18-24 months: This is considered a healthy birth spacing interval that allows the mother's body to recover, and is not a risk factor.
Therefore, the valid pregnancy risk factors are (B), (C), and (D) only.
Step 3: Final Answer:
The parameters that constitute risk factors for pregnancy are (B), (C) and (D) only.