**Core Concept**
The question requires knowledge of the safe contraceptive options in patients with sickle cell anaemia, a genetic disorder that affects haemoglobin production and increases the risk of complications during pregnancy. The underlying principle is to select a contraceptive method that does not further increase the risk of complications in patients with sickle cell anaemia.

**Why the Correct Answer is Right**
The correct answer is the barrier method because it does not affect the menstrual cycle or increase the risk of sickling crises, which are episodes of pain and other complications associated with sickle cell anaemia. Barrier methods, such as condoms and diaphragms, work by preventing sperm from meeting the egg, rather than affecting hormone levels or menstrual bleeding. This makes them a safe and effective option for women with sickle cell anaemia who are trying to prevent pregnancy.

**Why Each Wrong Option is Incorrect**
**Option A:** Oral 'Pill' is incorrect because it can affect menstrual bleeding and increase the risk of thrombosis, which is a concern in patients with sickle cell anaemia who are already at risk of blood clots.

**Option B:** IUCD is incorrect because it can cause pelvic infections, which are more common in patients with sickle cell anaemia who may have a weakened immune system due to chronic anaemia.

**Option D:** Progestin only pill or implant is incorrect because, although it may be a safer option than combined hormonal contraceptives, it can still affect menstrual bleeding and increase the risk of thrombosis, which is a concern in patients with sickle cell anaemia.

**Clinical Pearl / High-Yield Fact**
In patients with sickle cell anaemia, it's essential to choose a contraceptive method that does not increase the risk of complications, such as sickling crises, thrombosis, or pelvic infections. Always consider the individual patient's medical history and risk factors when selecting a contraceptive method.

**✓ Correct Answer:** C. Barrier method.