Amniotic Fluid Index (AFI) - Normal Values & Interpretation

What is AFI?

Normal Values

• Median AFI is approximately 14 cm from weeks 20-35, after which it begins to decline toward term.
• Campbell-Walsh Urology cites normal AFI as 8 to 18 cm, with oligohydramnios < 5-6 and polyhydramnios 20-24.

Technique

1. Patient supine; transducer held perpendicular to floor and aligned longitudinally with mother's spine.
2. Divide uterus into 4 quadrants (umbilicus = horizontal landmark; linea nigra = vertical landmark).
3. Measure the largest vertical fluid pocket in each quadrant (do NOT include umbilical cord - use color Doppler if needed).
4. Sum the 4 values = AFI.
5. If AFI < 8 cm, repeat the four-quadrant measurement to confirm.

Abnormal Values and Clinical Significance

• ~83% of cases (excluding PROM) are associated with fetal IUGR, though only 16% of IUGR fetuses have oligohydramnios
• Causes: PROM, urinary tract anomalies, placental insufficiency
• Associated with: fetal heart rate abnormalities, depressed Apgar scores, meconium passage in labor
• In early-onset FGR, AFI < 5 cm was present in 89% of intrauterine demises
• At term: usually an indication for delivery

• Etiologies: idiopathic (35%), diabetes mellitus (25%), congenital anomalies (20%), erythroblastosis fetalis (12%), multiple gestation (9%)
• Associated with: abnormal fetal lie, operative delivery, placental abruption

AFI vs. Single Deepest Pocket (SDP)

AFI in the Biophysical Profile (BPP)

Cesarean Section - Step-by-Step Technique (LSCS)

Pre-operative Preparation

1. Patient positioning - Supine with left lateral tilt (15°) to relieve aortocaval compression. Insert an indwelling urinary catheter (IDC).
2. Anesthesia - Spinal (preferred), epidural, or general anesthesia.
3. IV antibiotics - 2 g IV Cefazolin given 15-60 minutes before skin incision (reduces wound infection and endometritis).
4. VTE prophylaxis - TED stockings; consider LMWH.
5. Skin prep - Chlorhexidine-alcohol antiseptic preparation, allowed to dry before draping. Vaginal prep with iodine in emergency cases.

Surgical Steps

STEP 1 - Skin Incision

• Pfannenstiel (transverse): Most common. Curved incision ~3 cm above the pubic symphysis, or
• Joel-Cohen technique: Straight incision 3 cm below the level of the anterior superior iliac spines (ASIS). Associated with less blood loss and faster entry.
• Midline vertical (infraumbilical): Used in emergencies (including perimortem CS), obesity, or when rapid access is needed. The linea nigra (hyperpigmented midline) guides the incision.

STEP 2 - Subcutaneous Fat / Fascia (Rectus Sheath)

• Sharp entry through the middle 3 cm of subcutaneous fat and anterior rectus sheath.
• Fascia is incised transversely and then extended laterally by blunt dissection (Joel-Cohen) or by cutting with scissors (Pfannenstiel).
• The fascial edges are separated superiorly and inferiorly from the rectus abdominis muscles.

STEP 3 - Rectus Muscle Separation

• The rectus abdominis muscles are separated in the midline (not cut) by blunt dissection and retracted laterally.

STEP 4 - Peritoneum Entry

• The parietal peritoneum is identified and opened bluntly (fingers) or sharply with scissors, high up to avoid the bladder (especially important in repeat CS or advanced labor when the bladder may be elevated).
• The peritoneal opening is extended superiorly and inferiorly.

STEP 5 - Bladder Flap (Vesico-Uterine Peritoneum)

• The loose utero-vesical peritoneum is identified and opened ~2 cm below its fixed uterine attachment in the midline, then extended laterally.
• The bladder is bluntly reflected downward off the lower uterine segment (LUS) using a finger or gauze. In the presence of adhesions, sharp dissection is used.
• A bladder retractor is placed to protect the bladder.

Awaiting onset of labor first thins the LUS - this reduces blood loss and facilitates bladder flap development. (Creasy & Resnik's MFM)

STEP 6 - Uterine Incision

• A small 2-3 cm horizontal sharp incision is made on the LUS in the midline.
• This is then extended bluntly (fingers in a cephalad-caudad or lateral direction) to create a full transverse incision - reduces risk of extending into uterine vessels.
• For classical (vertical) uterine incision: used when LUS is poorly formed (< 28 weeks), placenta previa on anterior wall, transverse lie with back down, or emergencies.

STEP 7 - Delivery of the Baby

• Cephalic presentation: The surgeon's hand is inserted below the fetal head to flex and elevate it through the uterine incision. The assistant applies fundal pressure simultaneously. Forceps may be used if the head is high (elective CS).
• Breech presentation: Feet are grasped and breech extraction performed.
• The umbilical cord is clamped and cut between two clamps.
• The baby is handed to the neonatologist/midwife.

STEP 8 - Oxytocin Administration

• Oxytocin infusion (e.g., 5 IU slow IV bolus or 10-40 IU infusion) given immediately after baby delivery to reduce risk of PPH and aid placental separation.

STEP 9 - Delivery of the Placenta

• Spontaneous/controlled cord traction preferred over manual removal (less endometritis risk).
• Fundal massage + controlled cord traction are used.
• The uterine cavity is inspected and wiped clean with a moist swab.

STEP 10 - Uterine Closure

• Green-Armytage forceps are placed on the upper and lower edges of the uterine incision to identify the angles clearly (the lower edge can recede inferiorly and be difficult to find).
• The angles are usually secured first.
• The uterus is closed in 1 or 2 layers using continuous absorbable suture (No. 0 or 1 Vicryl/chromic catgut).
• Single vs. double layer remains debated - double layer may be preferred for women considering future pregnancies due to stronger scar.
• The vesico-uterine peritoneum (bladder flap) may or may not be re-approximated (non-closure has not been shown to be harmful).

STEP 11 - Hemostasis Check

• Inspect for bleeding from uterine angles, broad ligament, ovaries, and bladder.
• Count swabs and instruments.

STEP 12 - Peritoneal Closure (optional)

• Visceral and parietal peritoneum closure is not mandatory - evidence shows non-closure causes no harm and may reduce operating time and adhesions.

STEP 13 - Fascial / Muscle Layer Closure

• Rectus muscles fall back into place (not sutured).
• The anterior rectus sheath (fascia) is closed with continuous absorbable suture (e.g., loop PDS or Vicryl No. 1).

STEP 14 - Subcutaneous Layer

• If > 2 cm of subcutaneous fat, a subcutaneous layer closure reduces wound complications.

STEP 15 - Skin Closure

• Subcuticular suture (Monocryl) or surgical staples.
• Dressing applied.

Post-operative Care

• Monitor vitals, uterine tone, lochia, urine output.
• Early mobilization.
• VTE prophylaxis (LMWH + TED stockings).
• Analgesia (paracetamol + NSAIDs ± opioids).
• Breastfeeding support.

Types of Uterine Incisions - Summary