I appreciate your query.
Decrease in the amount of amniotic fluid level during pregnancy is called oligohydramnios
You have not mentioned the degree of oligohydramnios, which is assessed by the AFI ( amniotic fluid index
Severe degree is typically caused by fetal urinary tract
abnormalities such as unilateral renal agenesis
( Potter's syndrome ), fetal polycystic kidneys
, or genitourinary obstruction. Uteroplacental insufficiency is another common cause.
So your sonologist should rule out any fetal anomalies, or placental problems in your case. Also, your Blood pressure and other tests such as hemoglobin, blood sugar levels etc should be normal.
Minor degrees may also occur simply due to dehydration
of the mother, or without a determinable cause (idiopathic).
Also, I hope you have not had any leakage of fluid per vaginum, as that might cause oligo.
Regarding the cord around neck, you need not worry at 28 weeks, as it might cause problems only during labour, that too ones that can be diagnosed easily.
Maternal hydration has been shown to significantly improve the amniotic fluid levels, and that is the maximum that you can do at this stage.
Increase your fluid intake ( water, clear soups, juice, coconut water ) to atleast 4 - 5 litres per day.
You might also take essential amino acid
Intractable oligohydramnios might require intravenous hydration.
Monitor the baby with serial ultrasounds, AFI estimations and Colour doppler
All the best.