In the first two to three years after menarche, cycles often shift in flow, colour and length, and exam stress is a well-known trigger for a lighter or darker period. Dark, thick blood usually reflects slower shedding, and one such cycle in a teenager is not a concern on its own.
Next Steps
Track your daughter's next two cycles for flow and duration; if the pattern keeps changing, an adolescent gynaecology visit will help.
Health Tips
Do watch out for sudden very heavy flow or severe pain, both of which need earlier evaluation.